In the case of an attic installation your tv antenna will be sheltered from the environment so there s no need to ground it for that reason.
Do you need to ground an antenna in the attic.
Agreeing with adtech i don t see the nec requiring you to ground an indoor antenna system.
However the connection of your antenna coax to various ac operated equipment in this case your converter box or tv introduces the potential of electric shock.
To answer the question yes you can install your outside antenna in the attic if needed.
Antennas mine are receive only for fm tv and public safety bands will be generally restricted to the attic.
This isn t the ideal situation for installation of an outside antenna but sometimes it is necessary based on a number of factors.