The fire burned 80 percent of an office at the Salman Alfarisi Islamic Center, where Mohamed Osman Mohamud, 19, sometimes worshipped.
Mohamud is charged with attempted use of a weapon of mass destruction. He has pleaded not guilty.
Mohamud is accused of plotting to carry out a terror attack last Friday on a crowd of thousands during a Christmas tree lighting ceremony at Portland's Pioneer Courthouse Square.
