The structure of the National Security Council has varied under various presidential administrations. In the Nixon Administration, there were two cabinet members on the council: The Secretary of State and the Secretary of Defense.
Under the Obama Administration, three Cabinet members joined the Vice-President on the National Security Council: The Secretary of State, the Secretary of Defense, and the Secretary of the Treasury.
At present, under the Trump Administration, four Cabinet members are on the National Security Council: The Secretary of State, the Secretary of Defense, the Secretary of the Treasury, and the Secretary of Energy.