Police arrested anti-government activist Ekachai Hongkangwan on Friday, on a charge of causing harm to Her Majesty the Queen during her motorcade on Wednesday.
Mr Ekachai, 43, was taken into custody on Lat Phrao Road near the Imperial Lat Phrao store on Friday morning and escorted to Lat Phrao police station.
He was charged under Section 110 of the Criminal Code with causing harm to Her Majesty the Queen's liberty when the motorcade of Her Majesty the Queen and His Royal Highness Prince Dipangkorn Rasmijoti travelled past demonstrators outside Government House on Wednesday afternoon.
Mr Ekachai and another demonstrator, Boonkueanoon Paothong, were subjects of arrest warrants in this matter.
Mr Ekachai said he was arrested on his way to turn himself in at Dusit police station. Mr Boonkueanoon surrendered at Dusit police station.
The offence, carries a maximum penalty of life imprisonment.
Section 110 states: Whoever commits an act of violence against the Queen or Her liberty, the Heir-apparent or His liberty, or the Regent or his/her liberty, shall be punished with imprisonment for life or imprisonment of sixteen to twenty years. Whoever attempts to commit such offence shall be liable to the same punishment.
Over the past three days of demonstrations, police have arrested 22 protesters, comprising four rally leaders and 18 followers, according to Pol Maj Gen Piya Tawichai, deputy commissioner of the Metropolitan Police Bureau, and deputy police spokesman Pol Col Kissana Phathanacharoen.
They warned that more rallies would violate the ban on public gatherings of five people or more under the state of emergency declared on Thursday morning. Police would prosecute offenders.
According announcements on social media, a fresh demonstration was planned for Ratchaprasong intersection at 3pm on Friday.