The suspect was detained by an armed police officer traveling on the train, the local broadcaster reported.
French police officers were recently allowed to travel by train carrying their guns. The reform was designed to improve security on public transport.
Around one hundred law enforcement officers were mobilized to respond to the bomb threat, French media said. The train was stopped at one of the stations along its route, and passengers were evacuated. After a thorough check, no explosive devices were found on the train.
The suspect was put under arrest and the prosecutor's office of the city of Metz started an investigation into the incident. The SNCF railroad company announced that the incident caused an hour and a half's delay to the train schedule, according to the media report.