From the vantage of actual physics, anti-gravity would literally consist of neutralizing the curvature of spacetime created by objects with mass. Or otherwise put, anti-gravity technology would be warping spacetime back into a shape similar and equivalent to what it would be like if the object with mass responsible for gravity were not present, because that's what gravity is: it's a warping of spacetime.
Furthermore, celestial bodies like asteroids, moons, planets, stars, solar systems, galaxies and black holes are not just warping spacetime by way of gravity, but also by way of their rotation, which causes an effect called frame-dragging, which was predicted by Albert Einstein and proven to be factual by way of the data gathered by the two Gravity Probes that were sent up in the early 2000s, specifically so as to verify whether Einstein's predictions were correct. And they were.