A Bangkok Post reporter confirmed that shots were heard about 2.40pm and a demonstrator was hit in the leg by a bullet.
The injured protester was sent to Ramathibodi Hospital, BlueSky reported.
The gunman was arrested by protest guards and beaten while trying to escape vengeful protesters, it said, adding that he was sent to Rajavithi Hospital.
The PDRC is holding a rally outside the club against the Feb 2 election. Caretaker Prime Minister Yingluck Shinawatra and the Election Commission were holding talks at the Army Club today to decide the fate of the poll.
BlueSky TV also showed pictures of the alleged gunman's motorcycle, reporting it was registered under a policeman's name.
The channel also showed pictures of a Bang Sue motorcycle taxi queue jacket, number 15, said to have been discarded by the gunman as he fled.