Pouria Nour Mohammad Mehrdad, 19, was travelling on an Austrian passport earlier reported stolen in Thailand, police Inspector General Khalid Abu Bakar said.
Based on consultations with foreign intelligence services, he did not appear to be a member of any terrorist organisation and was apparently trying to migrate to Germany, Mr Khalid said.
Thai authorities have discovered that the tickets of two people who travelled on flight MH370 used the stolen passports of an Italian and an Austrian - both documents were reported lost in Thailand.
The two passports in question belong to Italian national Luigi Maraldi and Austrian Christian Kozel.
Meanwhile, the search for the missing plane, flight MH370, was expanded Tuesday to include more areas that were not on its flight path.
The passenger jet with 239 people on board disappeared en route from Kuala Lumpur to Beijing early on Saturday morning.