That was E.E. "Doc" Smith's assumption in the Lensman series when "negaspheres" were developed (planetary scale antimatter objects), in Grey Lensman written circa 1939. They had an "opposite 'gravitational charge'", a tractor beam would repel them while a pressor beam would pull them in, etc. It would be amusing if this turned out to be true (well, ignoring the yet to be if ever invented beam technology).