The man was identified as Abdusataar Abdulrehman and he was charged with illegal possession of military hardware.
"He is Uighur according to his passport," national police spokesman Prawut Thavornsiri said.
Thai authorities have arrested two suspects in connection with the twin bombings last month.
One of them, Mieraili Yusufu, identified the alleged mastermind as Abdulrahman, also known by the aliases Abdusataar and Izan. Izan left Thailand on a Bangladesh-bound flight on August 16, a day before the bombing.
Thai officials believe Izan left Bangkok for Bangladesh and from there to China.
Two bomb blasts rocked Bangkok last month. One of them targeted the Erawan Brahma Shrine on August 17, killing 20 people and injuring more than 100 others.
