Police arrested five men under the Terrorism Act on Tuesday in Birmingham in central England.
The suspects were arrested on suspicion of being involved in the commission, preparation or instigation of an act of terrorism. The men were between 29 and 36 years old, West Midlands Police said.
No details of the suspected activity were disclosed.
The arrests followed a long investigation, police said. The authorities are not seeking any other suspects. There was no immediate threat to the public, police said.