A 43-year-old Thai man, Kamon Somana, who rented the room in northern Chiang Rai province where the weapons were found, has been arrested, authorities said.
"We are investigating where weapons came from and where they were destined," Chiang Rai police chief Surachet Thopunyanond told AFP. "But we believe they were to be sent to minority groups on the border in exchange for drugs."
The suspect was charged with arms possession and smuggling, which he denies.
Myanmar's borderlands have been plagued by decades of civil war and experts say ethnic minority rebels use profits from narcotics to fund their operations.