Is Mica non-conductive?
completely non conductive 


no such thing exists, only "only conductive by a degree negligible to my problem".

But yes, Mica has an extremely low conductance. We technically call it an isolator, and Mica plates are commonly used as thermally-conducting, electrically-isolating spacers.

Of course, that quality doesn't apply to the rest of the components in makeups and body lotions, so if you got body lotion in your PC, clean it and hope for the best.


  Or should I be more concerned about regular household dust since it can carry static electricity? 


Any body can "carry" static electricity. That's actually called a charge. So, there's nothing special about dust here.

You'll also notice that w.r.t. to most properties the main difference between makeup powder and dust is whether you'd put it on your face.