Cause is unknown. Trembling of an eyelid, which happens in normal people, is called myokymia (an involuntary, spontaneous, quivering of a few muscle cell bundles within a muscle). Myokymia starts and stops spontaneously. In the eyelids, it can last a few minutes to a few days. One should see an ophthalmologist (md eye doctor) if such symptoms persist, keep recurring, or are combined with any other symptoms.
Benign tic. I get that, too. Irritation of one of the small muscle fibers in the eyelid. Some say coffee makes it worse. Not to worry.
Eyelid fasciculation. Sounds like may be benign eyelid fasciculations or twitches. However this is a diagnosis of exclusion if there are no underlying other causes (also look for entire face spasms). If it is very tiny eyelid twitches and eventually resolves on its own, it's likely not worrisome. See if induced by stress, lack of sleep, caffeine, etc.