According to the reports, a group of demonstrators attempted to enter the Sport Building 2 about 10am. A team of police used their shields to push them back.
Core members of the anti-government Student and People Network for Thailand's Reform (STR) later issued orders over a loudspeaker telling the protesters to stop fighting and instructing the STR guards to help break up the fight.
A television report said one protester was injured in the clash.
Election Commission (EC) member Somchai Srisuthiyakorn said it was likely that the candidacy registration for the Feb 2 general election will have to be postponed again following clashes between protesters and police this morning.
Mr Somchai, who oversees election administration, said the commissioners will meet to assess the situation today.