The fencing is part of beefed-up security measures designed to protect the building.
A rally is planned for Saturday in support of the people who stormed the Capitol on January 6.
The Department of Homeland Security expects 700 people to attend.
The district is worried protesters will bring guns to the rally.
D.C. Mayor Muriel Bowser has not requested the National Guard, but that still could happen.
The fence around the Capitol is expected to come down Sunday.