I heard that nystagmus is involuntary. but i can shake my eyes! is it a neurological condition?

Yes: Nystagmus is a complicated condition with many causes ranging from congenital to acquired and is involuntary. We do, however, have the normal ability to generate voluntary forced movements of our own eyes, called saccades, and can mimic nystagmus, however, the velocities and implicit times in generating voluntary saccades are much less than those of involuntary pursuit movements and nystagmus.

No: Some have developed the ability to shake the eyes as a combination of near focus and concentration. This is voluntary and does not harm the eyes. Some have perfected it as a performance trick.