Five Thai students who flashed a salute inspired by Hollywood film series The Hunger Games at Prime Minister Prayuth Chan-Ocha have been detained.
The three-fingered salute was widely used by protesters against Thailand's military coup in May.
The military had threatened in June to arrest anyone who refused to stop doing it when challenged.
Gen Prayuth led the coup, which came after months of political deadlock and unrest, and became PM in August.
On Wednesday, he was speaking at an event in the north-eastern province of Khon Kaen when five students from a local university sitting near the podium stood up.
They removed their shirts to reveal T-shirts underneath with a Thai slogan reading "No Coup", and flashed the three-fingered salute.
Police officers and soldiers immediately took the five away.
The three-finger gesture is used by characters in the dystopian Hunger Games film and book trilogy as a sign of silent dissent against a brutal authoritarian state.
It became so popular after the Thai coup that the authorities warned they would arrest anyone in a large group who gave the salute and refused to lower their arm when ordered.
Local media reported that Mr Chan-ocha appeared unperturbed on Wednesday and asked: "Does anyone else want to protest?" He added that protesters could lodge complaints with local government offices.
Army officials later confirmed that the students were taken to a military camp and were detained for "attitude adjustment", reported The Nation.
Lawyer Sasinan Thamnithinan said they had not been charged, the Associated Press reports.
Anti-coup leaflets had reportedly been distributed around Khon Kaen province before Gen Prayuth's arrival.
The area is known to be a power base for former PM Thaksin Shinawatra and his Pheu Thai party, whose supporters are known as "red shirts".
The military has been heavily criticised for its ousting of the democratically-elected civilian government.
But it has argued that its 22 May coup was necessary to bring peace and stability to Thailand, which saw violent clashes between red shirts and the pro-monarchy opposition "yellow shirts" supporters.
Gen Prayuth became prime minister after he was named by a legislature hand-picked by the military.
Amnesty International has said the military government has since engaged in widespread human rights violations, including arbitrary detentions and a clampdown on free speech.
The military has said it eventually plans to hand power back to civilians and promised to hold a general election in late 2015. But international players have raised concerns of the junta consolidating power in the meantime.