Somyot's magazine published the controversial articles in 2010, during severe political unrest in Bangkok. He was a member of the Red Shirts, a group that held anti-government protests and clashed with Thai security forces.
The Red Shirts support former Prime Minister Thaksin Shinawatra, who was ousted in a bloodless military coup in 2006.
It is not possible to report details of the content of the articles in question since they have been deemed to violate Thai law.
Thailand's King Bhumibol Adulyadej, 85, is the world's longest reigning monarch.
The country abolished absolute monarchy in the 1930s, and the king wields little political power. Still, the king -- formally crowned on May 5, 1950 -- is a deeply respected figure in Thailand and enjoys widespread popularity.
Human Rights Watch says there was a sharp increase in the number of lese majeste cases brought to trial in Thailand between January 2006 and May 2011.
Prosecutions have since decreased under Prime Minister Yingluck Shinawatra, Thaksin's sister who took office in 2011.
But authorities "continue to use draconian statutes in the Penal Code and the Computer Crime Act to restrict freedom of expression, including on the Internet," Human Rights Watch said.
Last year, a web editor received a 20,000 baht (US $628) fine and an eight-month suspended sentence for not deleting posts deemed critical of the monarchy quickly enough.