EXHIBIT 99

15985 East High Street

P. O. Box 35

Middlefield, Ohio 44062

Phone: 440/632-1666 FAX: 440/632-1700

www.middlefieldbank.com

PRESS RELEASE

Executive Vice President/Chief Operating Officer

(440) 632-1666 Ext. 3219

jheslop@middlefieldbank.com

Middlefield Banc Corp. First Quarter Earnings Increase 52% to $1.5 million

MIDDLEFIELD, OHIO, April 24, 2012 ¿¿¿¿ Middlefield Banc Corp. (OTCQB: MBCN), reported net income of $1.523 million for the quarter ended March 31, 2012, compared to $1.002 million for the quarter ended March 31, 2011, an increase of 52%. On a per share basis, the Company’s diluted earnings were $0.86 for the 2012 first quarter, as compared to $0.62 for the comparable period of 2011.

Annualized returns on average equity (“ROE”) and average assets (“ROA”) for the 2012 quarter were 12.81% and 0.94%, respectively, compared with 10.50% and 0.63% for the first quarter of 2011.

For the first three months of 2012, net interest income increased $528,000, or 10.5% from the same period last year. While interest income experienced a decline of $127,000, or 1.7%, interest expense was $655,000, or 28.0%, lower in the 2012 quarter as compared to the same period of 2011. The net interest margin for the three months ended March 31, 2012 was 3.89%, compared to 3.68% for the same period of the prior year.

For the three months ended March 31, 2012, management provided $600,000 to the allowance for loan losses, which compares to $865,000 for the same period of 2011. Net charge-offs for the 2012 first quarter were $152,000, or 0.04% of average loans. The allowance for loan losses at March 31, 2012 stood at $7.3 million, or 1.80% of total loans. At March 31, 2011, the allowance for loan losses was $6.7 million, representing 1.78% of total loans. Based on the evaluation of the adequacy of the allowance for loan losses, management believes that, at March 31, 2012, the allowance for loan losses was adequate and reflects probable losses in the loan portfolio.

Noninterest income for the first quarter of 2012 was $794,000. This was a modest increase of 13.6% from the comparable period of 2011. The primary factors in this increase were higher revenues from investment services and fees generated by increased debit card usage. Although deposit service charges increased year-over-year, the growth was tempered by rules eliminating certain automatic overdraft protection arrangements and the ability to charge fees for the payment of overdrafts for debit and ATM card transactions.

Noninterest expense for the first quarter of 2012 totaled $3.8 million, an increase of $77,000, or 2.1% from the same period last year. Salaries and benefits, the company’s largest noninterest expense, contributed $60,000 to the increase. This increase is largely related to the growth of the company, including increased staffing levels in regulatory compliance. Higher data processing costs and FDIC insurance expense were directly related to the growth of the company since the first quarter of 2011. The limited growth in non-interest expense reflects management’s on-going efforts to control expenses.

“Having finished a record earnings year in 2011, we are very pleased to report continued strong earnings during the first quarter of 2012”, stated Thomas G. Caldwell, President and Chief Executive Officer, “We enjoyed positive growth in net interest income, while maintaining our focus on managing our non-interest expenses.”

“Our efforts during the quarter are further evidenced by our efficiency ratio, which is very positive for a community-based financial company. We are especially pleased that we achieved these results even as we increased staffing in an effort to address the increasing regulatory burden. Our focus remains on delivering excellence in customer service, increasing value to our shareholders, and operating our company in accordance with safe and sound banking practices,” Caldwell concluded.

Balance Sheet Growth

The company’s total assets as of March 31, 2012 stood at $657.9 million, an increase of 0.5% over the $654.6 million in total assets reported at December 31, 2011. Net loans at March 31, 2012, were $397.0 million, up $1.9 million, or 0.5%, over the $395.1 million reported at December 31, 2011. Total deposits at the end of the first quarter 2012 were $583.9 million, or 0.5 % greater than the deposit level of $581.0 million at December 31, 2011. Stockholders’ equity at March 31, 2012, was $48.5 million. Tangible book value per share as of March 31, 2012, was $24.78.

Dividends

During the first quarter of both 2012 and 2011, Middlefield paid cash dividends of $0.26 per share.

Middlefield Banc Corp. headquartered in Middlefield, Ohio is a multi-bank holding company with total assets of $657.9 million. The company’s lead bank, The Middlefield Banking Company, operates full service banking centers and a UVEST Financial Services^® brokerage office serving Chardon, Cortland, Garrettsville, Mantua, Middlefield, Newbury, and Orwell. The company also serves the central Ohio market through its Emerald Bank subsidiary, with offices in Dublin and Westerville, Ohio. Additional information is available at www.middlefieldbank.com and www.emeraldbank.com

This press release of Middlefield Banc Corp. and the reports Middlefield Banc Corp. files with the Securities and Exchange Commission often contain “forward-looking statements” relating to present or future trends or factors affecting the banking industry and, specifically, the financial operations, markets and products of Middlefield Banc Corp. These forward-looking statements involve certain risks and uncertainties. There are a number of important factors that could cause Middlefield Banc Corp.’s future results to differ materially from historical performance or projected performance. These factors include, but are not limited to: (1) a significant increase in competitive pressures among financial institutions; (2) changes in the interest rate environment that may reduce interest margins; (3) changes in prepayment speeds, charge-offs and loan loss provisions; (4) less favorable than expected general economic conditions; (5) legislative or regulatory changes that may adversely affect businesses in which Middlefield Banc Corp. is engaged; (6) technological issues which may adversely affect Middlefield Banc Corp.’s financial operations or customers; (7) changes in the securities markets; or (8) risk factors mentioned in the reports and registration statements Middlefield Banc Corp. files with the Securities and Exchange Commission. Middlefield Banc Corp. undertakes no obligation to release revisions to these forward-looking statements or to reflect events or circumstances after the date of this press release.

MIDDLEFIELD BANC CORP.

Consolidated Selected Financial Highlights

March 31, 2012 and 2011 and December 31, 2011

MIDDLEFIELD BANC CORP.

Consolidated Selected Financial Highlights

March 31, 2012 and 2011

(Dollar amounts in thousands)

(unaudited)

MIDDLEFIELD BANC CORP.

Consolidated Selected Financial Highlights

March 31, 2012 and 2011

(unaudited)