Government spokesman Thanakorn Wangboonkongchana said on Sunday he had tested positive for Covid-19.
Mr Thanakorn said despite the RT-PCR test showing he had contracted the disease, he had only very mild symptoms.
The spokesman said he had to work from home and did not specify when the test was carried out.
Prime Minister Prayut Chan-o-cha selected him to replace Anucha Burapachaisri as the government spokesman in August last year. He is known as a staunch defender of the coup leader-turned-premier.