The new patient arrived in Thailand via a land border with Malaysia earlier this week and has been in quarantine, said Panprapa Yongtrakul, a spokeswoman for the government's Centre for COVID-19 Situation Administration.
Local infections have significantly slowed and over the last two weeks, 43 of 52 new cases were Thais who had arrived from abroad, Panprapa added.
The coronavirus has killed 57 people in Thailand since it was first detected in January.