Seven including a woman held in UK anti-terrorism operation
The men, aged between 25 and 32, were taken into custody by unarmed officers in the Moseley, Sparkbrook, Sparkhill, Ward End and Balsall Heath areas of Birmingham, the police said.
They added that specialist teams were searching their homes and seven other properties in the city - six domestic and one commercial.
The woman, 22, was held on suspicion of failing to disclose information contrary to the Terrorism Act 2000.
West Midlands Police Assistant Chief Constable for security Marcus Beale said: "The operation is in its early stages so we are unable to go into detail at this time about the nature of the suspected offences.
"However, I believe it was necessary to take action at this time in order to ensure public safety".
The terrorism threat level in England, Wales and Scotland remains unchanged at "substantial" - meaning that an attack is a "strong possibility".