There was no sign of Democrat leader Abhisit Vejjajiva, who had said earlier he would attend.
Puchong Nutrawong, the EC's secretary general, said Mr Abhisit had informed the EC at the last minute he would not come.
Mr Puchong said he did not know whether the Democrat Party would send anyone to represent the party but the meeting would take place anyway.
An hour earlier, Luang Pu Buddha Issara led anti-government protesters to the hotel, demanding the EC put up a poster in the meeting room.
The poster says: "Thais won't go to the polls until reform takes place."
After EC officials showed him the photo as a confirmation they had put up the poster in the room, the senior monk left, according to Thai news media.