Columbus police have evacuated a 41-story state office tower and blocked alleys behind the building after a dog detected the scent of explosives on a van parked at the loading dock.
State Highway Patrol Lieutenant John Born says a male suspect is in custody.
An investigator with the Ohio attorney general's office says he and fellow employees at the James A- Rhodes State Office Tower were told to leave the building by the stairs but weren't told why.
No explosives have been found.
About 4,000 state employees work in Rhodes Tower, which houses the Ohio Supreme Court, attorney general's office and other state agencies. The evacuation was ordered about 2 p.m.
Governor Taft's spokesman says Taft was in his office in another building that's a block away. Spokesman Joe Andrews wouldn't say whether security has been increased around the governor.