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
The region has enjoyed its warmest day of the year and the hottest February day for five years.
A campaign has been launched to attract more American tourists to East Anglia by highlighting the region's links to the US military.
More than 13,000 primary school spaces are needed in Essex in the next two years.