Your antenna being the highest point of the house will now be the attachment of lightning. You still may want to ground it for the safety of your house. If you do not give the lightning a path to ground its self, it will use what ever it can find. This will usually result with a fire and blown out dry wall. I have attached a e how blurt as to why and how you may still want to ground.
http://www.ehow.com/how-does_4588127...ect-house.html