Of course President Obama was playing golf at the time at Ft. Belvoir in northern Virginia.
Check it out:

The U.S. Capitol was evacuated Saturday afternoon when a small plane flew into restricted air space over Washington, D.C.

Officials determined the pilot of the small aircraft accidentally flew into the restricted area but not before they issued an “Aircon Red” and evacuated the Capitol Building and the cluster of office buildings that sit on the 58-acre Capitol Hill grounds.

U.S. Capitol Police said the craft entered the airspace at about 1 p.m. local time and the pilot was not communicating with officials on the ground. The emergency order and the evacuation was ordered 36 minutes later.