Police arrested a man in central England on Thursday under anti-terrorism laws.
The arrest in the city of Birmingham came a day after eight British suspects appeared in court charged in a plot linked to security alerts at financial targets in New York, New Jersey and Washington.
An anti-terror police spokesman said Thursday's arrest was not related to this operation.
Daljinder Mattu, spokeswoman for the force that made Thursday's arrests, said: "A 19-year-old man has been arrested under Section 41 of the Terrorism Act for being involved in the commission, preparation or instigation of terrorist offences."
The Terrorism Act 2000 gave police greater powers to investigate terrorism and stop and search suspects. Mattu said two other men, aged 24 and 36, were arrested in the same area "in relation to immigration matters".
The nationalities of the three men were not immediately available.