The Justice Department is also involved in the investigation into the nation's largest mortgage lender, said the New York Times, which also cited anonymous sources who said they were not authorized to discuss ongoing criminal matters.
"We are not aware of any such investigation," Countrywide spokeswoman Susan Martin told the Times.
FBI spokesman Richard Kolko declined to confirm for the Times that an investigation had been opened.
Investigators are looking at evidence that may suggest that company executives knew their mortgage securities would see many more defaults than predicted in its public documents, one source told the Journal.
The inquiry is part of a larger probe involving as many as 15 companies and comes in the midst of the subprime mortgage crisis.
Bank of America Corp. is in the process of acquiring California-based Countrywide for about $4 billion in stock. Bank of America agreed to the acquisition in January, and the transaction is expected to close in the third quarter. A spokesman for Bank of America declined to comment.
Countrywide CEO Angelo Mozilo was one of three mortgage industry executives brought before a Congressional committee Friday to defend their exorbitant pay at a time the industry was reeling.
Congressional figures showed that Countrywide lost $1.2 billion in the third quarter of 2007 and another $422 million in the fourth quarter. The company's stock fell 80 percent between February and the end of the year.
During the same period, Mozilo received a $1.9 million salary, $20 million in stock awards contingent upon performance and sold $121 million in stock.