Officers searched three homes and a community centre in Sheffield and another house in Chesterfield yesterday in a pre-planned counter terrorism operation.
Four men, aged 22, 31, 36 and 41, were arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism under section 41 of the Terrorism Act 2000.
They are being held at a police station in West Yorkshire, where questioning is set to continue today.
In Sheffield, one home in Burngreave and the Fatima Community Centre in Brunswick Road in the same suburb were raided along with a home in Meersbrook and another in Stocksbridge yesterday morning.
Bomb disposal teams were deployed to the community centre and the house in Chesterfield as part of the operation.
The North East Counter Terrorism Unit said the raids were 'pre-planned' and 'intelligence led'.