Sulak Sivaraksa, one of the country's most renowned thinkers and social critics, is facing a lese majeste complaint for comments he made in a speech about King Naresuan, who ruled the Ayutthaya Kingdom 400 years ago.
The Prachatai website, citing a report in Chao Phraya News, said that Lt Gen Padung Niwatwan and Lt Gen Pittaya Wimalin filed the complaint at the Chanasongkram police station on Thursday.
The two army officers accused Mr Sulak of defaming King Naresuan during a public speech "Thai History: Construction and Deconstruction" on Oct 5 at Thammasat University in Bangkok.
Mr Sulak is a staunch royalist but has also been a critic of the lese majeste law, which has been used extensively in recent years.
Article 112 of the Criminal Code states: "Whoever defames, insults or threatens the King, Queen, Heir-apparent or Regent shall be punished (with) imprisonment of three to fifteen years."
In late 2013, the Supreme Court upheld a lese majeste conviction in which the defendant was found guilty of defaming King Rama IV, who reigned between 1851 and 1868.
"The ruling surprised lawyers and academics who have always understood that the law does not cover former kings," Prachatai said.
King Naresuan ruled the Ayutthaya Kingdom from 1590 to 1605 and was famed for his campaigns to free Siam from Burmese rule.
A series comprising five big-budget films, The Legend of King Naresuan, has been highly successful. Earlier this year the military junta staged free screenings of the movies as part of its "Returning Happiness to the People" campaign.