Unlikely actually.
Based on current understanding of gravity, it isn't possible to shield it. Of course, you can make the argument if another civilization was visiting us, they would have a technology far greater than ours. However, when it comes to gravity, we know some interesting details - it isn't a real force, it isn't like a technology which can switch on and off a magnetic field.
Gravity is a product of warping spacetime, if anything, a ship may be using a type of Alcuiberre drive, but I am quite certain it isn't anti-gravitational device. Supposing they are using some kind of electromagnetic technology then at best, it may have effects that are ''like'' an antigravity device. Perhaps then, one should call it, a pseudo-antigravity device.