depends on which sort. normal mushrooms are fine raw. they taste good too! but field mushrooms, for example, that you find in your back garden, i wouldn't risk eating too much of raw - just in case.
If you mean normal mushrooms from the supermarket, it's best to just brush them clean. Washing them with water makes them go slimey. Don't worry about getting every single bit of dirt off them, it won't do you any harm.