The company says the investigation began after it notified federal regulators there was a possible trading impropriety in a regulatory filing, and the bank says it is cooperating with the SEC.
The trading being investigated took place during 2002 in the $584-million First American Small Cap Growth Opportunities fund, a fund advised by U.S. Bancorp Asset Management.
A spokeswoman for U.S. Bancorp stated that the trades are neither related to market timing nor late trading.
U.S. Bancorp hired an outside law firm, Kirkpatrick & Lockhart to review trades, and it says the firm found that no employees at the bank violated securities laws.
As part of the ongoing mutual fund investigation, the SEC and the National Association of Securities Dealers (NASD) have also requesting information about mutual fund trades at Piper Jaffray Cos., which U.S. Bancorp spun off to shareholders in December.