A 21-year-old woman and two men, 27 and 21, whose identities have not been made public, were apprehended at their home in Walsall, a town near Birmingham in central England, Efe news agency reported.
Agents from the anti-terrorism unit were leading the operation which was conducted based on information from the secret service.
“There was no immediate threat to public safety. Searches are now being carried out in eight associated addresses in Walsall area and one in Moseley, Birmingham,” a police spokesman said.
The three suspects are being interrogated in the West Midlands police station, the spokesman added.
Under the anti-terrorism law, police officers have 48 hours to question suspects before either filing charges, releasing them or seeking judicial permission to extend detention.
British authorities have not hidden their concern about the increasing number of young Britons travelling to Syria to join the Islamic State Sunni radical group.