Tv Antenna Mounts In The Apt. I Moved Into, There's A Coaxial Cable Line That Is Connected To The Roof Tv Antenna....?

In the apt. I moved into, there's a coaxial cable line that is connected to the roof tv antenna....? - tv antenna mounts

Is it safe to use that line? If the ceiling mount antenna is not properly grounded, can damage my LCD TV in the case of lightning cause? How could I in a position to establish whether the line is based with a voltmeter or multimeter?