Although malware threats to the Mac have been minimal compared to the PC, for those desiring additional protection there are choices. Topher Kessler (CNET MacFixIt) recently commented on an analysis of the most common anti-virus products.
The antivirus tools used in the tests included a number of free and paid scanner packages from Avast, VirusBarrier, Sophos, Dr. Web, ESET, Kaspersky, F-Secure, ClamXav, Norton, MacKeeper, and its included Avira engine, among others.
See this link for more information: Popular security utilities for OS X put to the test