New bathroom mirror covers a junction box
If the wires are installed in a junction box, then wire nut them separately, wrap some electrical tape around them, insert them back into the junction box and cover the box with an approved cover plate. If they are just dangling out of a hole in the drywall/tile, then you need to find out what junction box they come from, probably a switch box, and disconnect then there. Wire nut and tape them and maybe leave a note explaining what they're for.