A bomb disposal team was put on standby at the request of Scottish police, a defense ministry spokesman said.
"This is not a fire, escape of gas, anything like that. It's just precautionary measures being put in place," the Royal Air Force said in a statement. Employees were being taken by helicopter to other rigs in the North Sea.
Sky News television reported that an explosive device was found on the rig, and that comments by one employee sparked the security alert.