Spokesman Col Winthai Suvaree said the cause of the crash of the twin-engine Bell 212 helicopter was not immediately known.
He said the aircraft crashed 10 minutes after taking off from an army camp in Phayao province, about 590 kilometers north of Bangkok.
Those killed included Maj Gen Songphol Thongjeen, the newly promoted deputy commander of Thailand's northern army region.
The officers on the helicopter had finished an inspection mission in Phayao and were returning to an army base in another province.