The teenager was detained at around 2.30pm on Tuesday as he was trying to leave the UK, the Metropolitan Police said.
He is being questioned on suspicion of preparation of acts of terrorism, dissemination of terrorist publications and inviting support for a proscribed organisation.
Officers were searching an address in north London following his arrest.
The man was detained under the Police and Criminal Evidence Act (PACE).
The Met said the arrest does not relate to offences against the UK.