My parrot is rolling on his back and walking around the bottom of cage trying to bite each part of the cage. Is this normal behavior or should I be worried?
Did this just begin? How many years have you had the bird?
No, this is not normal behavior. If your bird is new, maybe it is just flipping out and trying to find an escape, but other than that I can't think of a reason for a bird doing this.
It could be a reaction to something toxic. I suggest you Find an Avian Vet to examine your bird and bring a list of everything you clean with and any air fresheners etc.