Are you sure it's not just static? Touching it with your finger will earth it and thus discharge it, so if it is static, then once you've touched it, it should not give you another belt if you touch it again. Also ensure you turn the TV off & wait a few minutes before touching it. Older TV's do generate a large amount of static, which could be leaking through the screened braid of the aerial cable. But no, an aerial socket should not be carrying any voltage on the outer shielding.