Counter terrorism officers stopped a man at Stansted Airport on Sunday night.
He was arrested on Monday on suspicion of terrorism offences and has been taken to a London police station where he remains in custody.
The 21-year-old had returned to the UK from Istanbul, Turkey, via Stuttgart.
Detectives says the arrest was not in response to any immediate threat or risk. Detectives have carried out searches of three addresses in connection with this investigation.
More top news
Norwich City picked up their first Championship win of the season by beating QPR 2-0 at Carrow Road.
Christmas has arrived early in Northampton after one of the town theatres launched its panto - starring Union J singer Jaymi Hensley.
Dry weather and a growing population are putting severe pressure on East Anglia's water supplies.