FBI documents show that the agency investigated People for the Ethical Treatment of Animals in the late 1990s after hearing claims that the group was planning an anthrax attack.
The Virginian-Pilot says PETA obtained the documents earlier this year through a Freedom of Information Act request.
According to the documents, FBI investigators were told that PETA planned to release anthrax at the U.S. Army Medical Research Institute of Infectious Diseases in Washington, D.C.
PETA president Ingrid Newkirk tells the newspaper that the group didn't learn about the anthrax allegations until this year. She calls the allegations "total fantasy."
An FBI spokesman says the bureau doesn't discuss its investigations but that it has an obligation to look into such claims.