Is there a virus in team fortress 2

The actual game has no viruses unless you perhaps download it from an illegal source (i.e a torrent and crack website).

There is however a possibility, with some 3rd party servers (not the ones that VALVe hosts) they have the permission to do anything they like and may try to upload malware onto them and if you do join, it may download to your computer because you are joining as a client.

This is quite rare however and most servers like this are usually but with proper firewall tools, it's almost impossible for someone to hack you because of the redirected traffic. But the short answer is no, it's safe and you are most likely to enjoy a wholesome game with continuous updates and a gleaming community.