Crews from the Northern Ireland Fire and Rescue Service (NIFRS) are tackling the blaze on the Ballybogey Road. Part of the road is closed.
Liam O'Sullivan of the NIFRS said there were about 1,000 bales of hay in the barn.
He said it was a complex operation, with chemicals in an outlying shed.
Mr O'Sullivan said at this stage it was believed the fire was an accident.
More than 50 cows have been rescued from a fire at a barn near Ballymoney, County Antrim.