Three Thais returning from Tachilek were among 11 more coronavirus infections reported on Friday, taking the number of confirmed cases to 4,180.
The two women, who worked at an entertainment centre, and one man were in quarantine at Chiang Rai Prachanukroh Hospital.
The government has been urging Thai returning home to do so through the official checkpoint, instead of illegally crossing the border as many of them do, so the Covid-19 outbreak in Myanmar can be kept out of Thailand.
Elsewhere, there was one case in Phayao, three in Bangkok, one in Phichit, one in Ratchaburi and one in Sing Buri.
The cases coming from Tachilek caused alarm ahead of the holiday season.
Other cases incuded two Thai women returning from Saudi Arabia, two from Bahrain and another from Portugal.
A Swedish man, an American woman and a South Korean man had also tested positive after they arrived in the country.
Of the total 4,180 people diagnosed with Covid-19, 3,903 (93%) had recovered, including 15 discharged from hospitals over the past 24 hours, and 217 people remained in hospitals. The death toll was unchanged at 60.
