Most of the anti-virus products already have a version for Macs. My favorite, Avast!, has one...
http://www.avast.com/free-antivirus-mac
You don't need AV/Malware software for a Mac. There are a few exploits out there but they just try and trick you into installing something which you have to put in your password to do.
Originally Posted by hardnfast
Do not ever make the mistake that your Mac or Linux computer is immune. There is plenty of malicious code out there for both. Heard of the nasty stuff that gets into your web based email like Hotmail, Gmail, etc. and spams everyone in the contact list? Well remember that since those systems are web based and not on your computer it does not matter what kind of computer you have.