Election Commissioner Somchai Srisuthiyakor filed the first complaint under a new law meant to discourage campaigning against the draft charter, which will be put to a referendum on August 7.
The penalty for breaking the law is up to 10 years in prison and a fine of up to USD 5,715. The complaint was based on material on the Facebook page of a social group based in the northeastern province of Khon Kaen, a hotbed of dissident activity.
"People are allowed to post opinions agreeing or disagreeing with the new draft, but we encourage that they do so in an academic fashion with reason and logic, rather than using foul and strong language."
The law prohibits acts of unrest and campaigning with a provocative, aggressive or violent manner to influence voters, but Prime Minister Prayuth Chan-ocha and other officials have made clear they disapprove of any criticism.
Also Read
The government insists its own ambitious plans to publicize the charter's contents are strictly educational. Prayuth seized power in May 2014 after staging a coup against an elected government.
Thailand's Computer Crime Act has broad definitions that are often applied to expressions of political opinions.
Those arrested were taken for detention at army bases, where they can be held for a week without any charges.
"The capture of these people is not in accordance with either international or national laws," said Poonsuk Poonsukcharoen, a member of the Thai Lawyers for Human Rights group.
"The power that the army received from the new legislation to capture and detain people for expressing opinions against the draft constitution is being used in the wrong way. These arrests are creating a sense of fear among the public."