Depends on how you use your Mac...?
Personally I never have, but then I don't network in a Windows environment or share much more than a photo or two with Windows systems. So in essence, I'm not a risk of passing a virus from one Windows computer to another.
OS X Mac's don't get viruses like Windows PC's, but avoiding malware can be a challenge for those that like download all sorts of crapware to help there Mac run faster.
Have a look at > Thomas' Tech Corner » Mac Malware Guide