TV antenna moves a bit - problem?
It sounds like your antenna is for terrestrial broadcast TV, in which case it should be OK.  You want it to be facing the transmitter as squarely as possible, but a little bit of variance won't affect the signal reception too much.  If you have digital TV broadcasts in your area, you may not even notice anything at all.  Furthermore, if you do find that it's a problem, you can always secure it with wires later.

Satellite TV is more finicky: since the transmitter is much further away, you need to have the dish pointed more accurately.  But satellite dishes usually have a sturdy base, and are smaller than terrestrial antennas, so they don't move as much.