Anti-terrorism officers were questioning five men after completing searches at three homes.
West Midlands Police said the suspects, aged 29 to 36, were still being held in connection with a "long and complex" investigation by the region's Counter Terrorism Unit.
The men, arrested on suspicion of involvement in the commission, preparation or instigation of an act of terrorism, were detained at addresses in Birmingham on Tuesday.
A police spokesman said: "Officers continue to search three residential and two business properties following the arrest of five men under the Terrorism Act.
"The houses in the Bordesley Green, Hodge Hill and Sparkhill areas and the business premises in central Birmingham and Kenilworth are being examined by forensic specialists from the force's counter-terrorism unit."
Searches at three other home addresses in the Ward End, Stechford and Aston areas of Birmingham were completed on Tuesday night.
A large number of items were taken away for examination, the spokesman said.