Is it safe to mount TV on the wall over my fireplace?

It depends upon how hot the area where you plan to mount the TV gets. Get a pro to mount it for you. Mounting it through the wall will put it closer to the chimney, which is an even hotter area. That sort of installation may look inviting, I think you may be inviting trouble. Severe neck problems can be caused by constantly looking up. It would all depend on just how warm the wall gets with a good fire blazing. One can opt for a thermometer and tape it to the wall and see just how warm it gets while the fire is present. You can check with the manufacturer for the temperature range of the TV. Mounting it in the wall may not be possible with the flue present. Good Luck.