The closed door meeting of armed forces top brass, chaired by Gen Tanasak, will be held at the Supreme Command office in Chaeng Wattana, the source said.
Chiefs of staff of the army, navy and air force and officers in charge of operations will also attend the talks in addition to the three commanders-in-chief, with the political situation and the armed forces' position on the agenda, the source added.
The meeting is arranged ahead of a major rally by the red-shirt United Front for Democracy against Dictatorship (UDD) set for Saturday to protect caretaker Prime Minister Yingluck Shinawatra and her government.
Army commander-in-chief Prayuth Chan-ocha played down Wednesday's meeting, saying that the military leaders were already in close contact, although they did not meet regularly for talks.
Gen Prayuth reiterated the army's stance in staying neutral instead of being part of the conflict, as the red-shirts will mobilise supporters for a big gathering to counter the People's Democratic Reform Committee protests led by Suthep Thaugsuban.