Hi,
if you mean over a 3d or 2d object, you will need to have a collider, and then you can either have an fsm on that object that will respond to mouse enter and mouse exit events. else you will have to raycast.
if you mean a UI object, you currently only have the option to use an fsm on each of your UI element and catch pointer enter and exit. if you need a raycasting, let me know, I'll do the custom action necessary for this ( as the raycast as to come from the event system and not the physics engine)
Bye,
Jean