UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K/A

Amendment No. 1

ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended September 28, 2012

Commission file number: 001-31650

MINDSPEED TECHNOLOGIES, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code:

(949) 579-3000

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act:

None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes  ¨    No  x

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    Yes  ¨    No  x

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  x    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405 of this chapter) is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    x

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨    No  x

The aggregate market value of the registrant’s voting and non-voting stock held by non-affiliates of the registrant as of the end of its most recently completed second fiscal quarter was approximately $249.7 million. Shares held by each officer and director and each person owning more than 10% of the outstanding voting and non-voting stock have been excluded from this calculation because such persons may be deemed to be affiliates of the registrant. This determination of potential affiliate status is not necessarily a conclusive determination for other purposes. Shares held include shares of which certain of such persons disclaim beneficial ownership.

The number of outstanding shares of the registrant’s Common Stock as of November 23, 2012 was 41,725,343.

Documents Incorporated by Reference

Portions of the Registrant’s Proxy Statement for the 2013 Annual Meeting of Stockholders, to be filed pursuant to Regulation 14A within 120 days after the end of the 2012 fiscal year, are incorporated by reference into Part III of this Form 10-K/A.

EXPLANATORY NOTE

Mindspeed Technologies, Inc. (the “Company”) is filing this Amendment No. 1 on Form 10-K/A (“Amendment No. 1”) to its Annual Report on Form 10-K for the fiscal year ended September 28, 2012, which was originally filed with the Securities and Exchange Commission on December 12, 2012 (the “Original Filing”), to amend Item 15, Exhibits and Financial Statement Schedules, in order to correct a clerical error with the filing of Exhibit 23, Consent of Independent Registered Public Accounting Firm, and file the correct Exhibit 23 that had been issued to us by the Independent Registered Public Accounting Firm. Accordingly, this Amendment No. 1 consists solely of the preceding cover page, this explanatory note, the list of exhibits filed with this Amendment No. 1, and the signature page. Other than as noted herein, this Amendment No. 1 does not modify or update any disclosures made in the Original Filing or reflect events that may have occurred subsequent to the filing date of the Original Filing.

EXHIBITS FILED WITH THIS AMENDMENT NO. 1

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this Amendment No. 1 to Annual Report on Form 10-K/A to be signed on its behalf by the undersigned, thereunto duly authorized.

EXHIBIT INDEX