Not many details as of right now, but a man with what appears to have been a shotgun was arrested outside the Capitol, according to Reuters. No one has been injured.

This part is interesting, however:

Police with dogs cordoned off several blocks as a bomb squad inspected his pickup truck. Schneider told reporters there appeared to be “items of concern” inside the truck.

Update: The Hill has a bit more.

An unidentified white male carrying a shotgun and a bag of ammunition was arrested and taken into custody by Capitol Police after an officer spotted him walking toward the Capitol near First and D streets Northeast…

She added that the arrest involved more than one officer.