Anti-coup activist Jatupat Bunpattararaksa and five other people rejected charges Wednesday that they had defied the regime's ban on political gatherings of more than five people.
Police levelled the charges after Mr Jatupat, better known as Pai Dao Din, and the other activists were found to be involved in a protest against the draft charter in July.
The activists denied all charges after surrendering to police at Muang Khon Kaen police station Wednesday.
The five were identified as Chatmongkol Jenchiewchan, a member of the Dao Din anti-coup group; Narongrit Upachan, from the New Generation Citizen group; Nattaporn Artharn, from the northeastern New Democracy Movement; and Duangthip Kararit and Neeranuch Neamsab, both members of the Legal Centre for Human Rights.
The charges of breaching the National Council for Peace and Order's (NCPO) order banning political gatherings were brought against them and Mr Jatupat after they held a political event urging people to vote "no" to the draft charter ahead of the Aug 7 referendum at Khon Kaen University (KKU) on July 31.
The six were also questioned for more than two hours by a panel led by Muang Khon Kaen chief Noppadol Petchsut.
During questioning, police and plainclothes officers were deployed to maintain peace and order as other Dao Din members and KKU students gathered outside the station to support the suspects.
Speaking after the inquiry, Pol Col Noppadol said the suspects were temporarily released and would testify to police again on Oct 4.
Police also questioned a complainant, and various witnesses involved in the incident, he said.
Mr Jatupat said he and the other suspects were ready to fight in court and will provide evidence and documents relating to the case to police on Oct 4.
He said they were exercising their right to freedom of speech at the July event.
The six suspects also called on the NCPO to abolish the order which bans political gatherings of more than five people, revoke prosecutions against those who were involved in cases associated with expressing political opinions and also stop taking such cases to the military courts.