Einstein's Cosmological Constant acts as a sort of anti-gravity, but it doesn't really act in the same way as gravity itself does, and in areas of high gravity (e.g. near a star or black hole), there isn't a strong enough anti-gravity to counteract gravity.
In reality, there is no quantum theory of gravity (yet), and our most complete theory of gravity is General Relativity. According to GR, gravity isn't really a force, it's a curvature of spacetime, therefore it's a pseudo-force. It acts like a force in some cases, but it disappears if we find ourselves in an equilibrium state between gravity and centrifugal force (another pseudo-force), and we find ourselves in Zero-G. Since it's a pseudo-force, we shouldn't expect it to have an equal and opposite counteracting force.