The document, filed Thursday, did not specify what aspect of the lender the SEC's probe is focused on, although regulators launched an informal inquiry into Countrywide Chairman and CEO Angelo Mozilo's stock trades last fall.
Bank of America, which finalized its acquisition of Countrywide last month, also noted in the filing that Countrywide has responded to subpoenas from the SEC.
Representatives for Charlotte, N.C.-based Bank of America and Countrywide declined to comment beyond the filing Friday.
A call to an SEC spokeswoman in California was not immediately returned.
The Los Angeles Times reported Friday that the SEC probe centers on whether Mozilo's stock trades violated the law and whether the lender's financial disclosures misled investors.
The newspaper based its report on unnamed persons close to the investigation.
Mozilo, who is no longer with Countrywide, could not immediately be reached for comment.
Mozilo's trades of Countrywide stock began drawing negative attention last year as the company's stock price tumbled.
The executive exercised options on thousands of shares of common stock through a prearranged trading plan, but the timing of changes in the stock-selling program drew shareholder criticism.
The changes, which were made in the months before the company's stock plunged, allowed Mozilo to significantly increase his sales of Countrywide shares.
Mozilo has denied making any improper trades and has said he is cooperating with the SEC.
Since the collapse of the subprime mortgage market last summer, Countrywide has been hit with lawsuits by investors, consumers, and state officials in California, Illinois, Florida and Connecticut.
On Aug. 11, a U.S. Bankruptcy Court judge in Pittsburgh is set to review an agreement in which Countrywide agreed to pay a bankruptcy trustee $325,000 to settle allegations that the mortgage lender sought improper fees or payments from bankrupt homeowners and otherwise violated bankruptcy court orders and regulations in nearly 300 cases.
Countrywide acknowledged errors in handling some debts, but it had denied any systematic effort to thwart bankruptcy protections to collect money.
Countrywide is also among the companies being investigated by the FBI as part of the agency's probe into the financial services industry in the wake of the mortgage meltdown.
Shares of Bank of America rose 73 cents, or 2.3 percent, to $32.25 Friday.