The Cannon House Office Building at the U.S. Capitol was evacuated shortly after noon on Thursday when an alarm sounded.
The reason for the evacuation was not immediately clear. Fox News reported that officials believe a construction worker accidentally set off an alarm.
Streets nearby were closed as a result of the evacuation.
Rep. Nancy Mace, South Carolina Republican, posted a video of herself leaving the Cannon building.
“We’re being evacuated,” she said on Twitter as a shrill alarm sounded repeatedly. “We’re not really sure what’s going on — some kind of threat.”