Three men and a woman have been arrested in Coventry on suspicion of terrorism offences.
Two men, aged 26 and 18, and a 58-year-old woman were held on Tuesday, police said.
A 57-year-old man was arrested on Wednesday following the pre-planned operation, West Midlands Police said.
All four were taken to a police station for questioning and the force said there was not believed to be any imminent threat to the public.
A house in Kare Road, Wyken, was being searched by police and a blue forensics tent was erected outside.