U.S. Capitol police shot a male suspect Monday afternoon following reports of gunfire at the Capitol Visitors Center.
A female civilian bystander was injured by shrapnel, but no U.S. Capitol Police officers have been injured.
The Capitol complex remains on lockdown.
According to a notice sent to Senate staffers, and no other suspects appear to be at large.
"There has been an isolated incident at the U.S. Capitol. There is no active threat to the public," the D.C. Police Department tweeted.
Police and firefighters swarmed the entrance of the visitor center, which is packed this week with tourists, spring break visitors and school groups.
Congressional staffers were sent a notice to shelter in place, instructing them to lock doors and moved to assigned shelter areas. Those outside the buildings on the Capitol complex were told to "seek cover away from the area."
The White House was also briefly locked down after what appears to be an unrelated incident.
House Speaker Paul Ryan, who is not currently in Washington, has been briefed on the incident, according to his spokesman.
Senate Majority Leader Mitch McConnell is in Louisville and his staff is safe, his spokesman said.