The Hollywood star gave a speech on the steps of the building on Friday (16Mar12) before joining demonstrators but was seized after he ignored three warnings from cops to leave the area.
He was handcuffed and secured with cable ties before being led to a van with his father Nick, who was also arrested. They were then driven away by secret service officials.
Clooney was charged with disorderly crossing a police line - a misdemeanour - and was still being quizzed by law enforcement agents as WENN went to press.
The star has long been involved with raising awareness of the humanitarian crisis in the war-torn African republic. He travelled to the region last week (05Mar12) to witness its hunger crisis first-hand and to gather information before addressing members of Congress at the Senate Foreign Relations Committee on Wednesday (14Mar12).