There have been 1000000000 threads discussing this problem.
Check similar threads on bottom of page, or use search.
Anyway, true, there are MOSTLY no Linux viruses. You may or may not need an anti-virus depending on how you use your system. True, ClamAV is mostly used for checking mail, but it is not limited to that. True, most users use anti-viruses to scan for windows viruses, but not only for that.
Conclusion: it's up to you. If you see a linux virus, let me know about it, I'm curious to see it.