I personally do prefer to keep an antivirus program on my Linux box, mainly because I do do a lot of file-sharing with Windows users. Although Windows viruses won't run on Linux Mint, they will lie dormant, waiting to be passed on. I consider it a courtesy, as I don't particularly wish to cultivate a reputation for being a "Typhoid Mary"
My other reason for keeping antivirus is for scanning my seldom-used-now Windows drive, and the Windows machines on our household LAN. I've uncovered a couple of viruses that way, invisible to the Windows antivirus programs on those machines.
I use Avast! for Linux, which is available in .deb packages. Simply download the .debs from the Avast! site and double-click to install, they will install the GUI and add itself to MintMenu automagically now.
There IS Linux malware, though precious little 'in the wild'. http://en.wikipedia.org/wiki/Linux_malware
As Linux gets more popular (thanks to Ubuntu and M$'s greed and screw-ups), the possibility for exploitation may increase. However, I think the real work of antimalware for Linux is as noted above, using it to detect Windows viruses on Windows machines, that have hidden themselves from the Windows antimalware programs.