Despite being one of the strongest and most secure operating systems, Mac is not immune to attacks by malicious software. Even if you have a Mac, you should have an antivirus installed on your computer to protect it from external threats.
ClamXav has a great user interface that uses an open-source antivirus engine called ClamAV. UNIX users will be well acquainted with this tool that you operate via the command line. The program can run passively or actively and also lets you scan the entire hard drive or just a particular directory.
If you receive a lot of emails from users who run Windows or download applications for that operating system, ClamXav can scan them for viruses. You can also program it to do regular scans and monitor certain folders that may be more vulnerable to possible virus or malware infections.