The university's official Twitter account announced a "shelter in place" order was in effect at 7:55 p.m. EDT, and later tweeted a photo of two individuals and asked followers to call police if they are seen.
It is not believed to be an active shooter situation.
"In regards to claims that there is an active shooter on campus, American University's Department of Public Safety wants people to know that a citizen reported to campus police that they saw a man with a gun," the university wrote on its emergency alert page.
AU's Public Safety tweeted this photo of two individuals it is looking for:
This story is developing and will be updated as we get more details.