Passengers were being escorted from the plane, flight AI 379, in line with emergency plans, an Airports of Thailand official said.
No bomb was found on the aircraft after a preliminary search was completed, said the official.
The aircraft took off from Phuket airport for the Indian capital at 9.30am, but made a wide loop around the Andaman Sea and landed back at the Thai island at 11.38am, according to flight tracker Flightradar24.
A bomb threat note was reportedly recovered from the lavatory of the plane.
The passenger who found the note was being questioned, said the Thai airport official.
The incident follows the crash of an Air India flight in Ahmedabad on June 12 shortly after takeoff, in which more than 260 people on board and on the ground were killed.
Indian airlines and airports were inundated with hoax bomb threats in 2024, with nearly 1,000 hoax calls and messages received in the first 10 months, nearly 10 times that of 2023.