Why is there an exposed wire coming out of my wall near my fluorescent light fixture?
This is a ground wire.  No wires should be left exposed hanging out of the wall.  It's not going to spontaneously burn down your house like that, but it could possibly become energized in which case it would pose a risk if someone were to make contact with it.

The fixture should have a grounding nut and that wire should be secured to it. Look for a green colored screw (not guaranteed to be green, but makes finding it simple).  

In the event the wire really isn't needed, the wire should be neatly folded up within the electrical box (or the wiring box on the fixture itself).