U.S. Capitol Police arrested a congressional staffer who brought a handgun to a House of Representatives office building this morning.

Ryan Shucard, press secretary to Rep. Tom Marino, R-Pa., was arrested around 9:15 a.m. after police discovered a Smith & Wesson 9 mm handgun and magazine during an administrative search required to enter the Cannon House Office Building, Lt. Kimberly Schneider, a spokeswoman for the Capitol Police, confirmed to ABC News.

Shucard is charged with carrying a pistol without a license, which is a felony, and was processed at the Capitol Police headquarters, police said.

Marino's office has placed Shucard on indefinite unpaid leave while the investigation is ongoing, Marino's chief of staff Bill Tighe told ABC News. Marino has been notified of the incident, he said.

All indications from Capitol Police suggest Shucard accidentally brought the weapon onto Capitol grounds, Tighe said.

ABC News' John Parkinson contributed to this report.