The FBI raided the Maryland home of John Bolton, who served in President Donald Trump's first administration as national security adviser but later became critical of him.
The audit is related to an investigation into the handling of classified documents, a person familiar with the matter told The Associated Press on Friday.
According to the source, who spoke on condition of anonymity, Bolton has not been detained and has not been charged with any crime.
Bolton has served as Trump's third national security adviser for 17 months and has clashed with him on issues related to Iran, Afghanistan and North Korea.
He was under scrutiny during the first Trump administration for a book he wrote about his time in government, which officials claimed revealed classified information.
However, in 2021 the Justice Department dismissed the lawsuit and closed a separate investigation by a grand jury.
On the first day of his term this year, Trump stripped the security clearances of more than 40 former intelligence officials, including Bolton.
He was also among three other former Trump officials who had their bodyguards revoked this year.