You really don't need anti-virus on a mac. I have two video editors at work. One a mac pro running Yosemite with Adblock Plus and Ghostery as browser extensions as my preventive measures. If you absolutely must run anti-virus ClamXav is a stand-a-lone scanner that only runs if you start it.
On my Windows 7 editor I have Avast! anti-virus backed up by weekly scans with Malwarebytes. Wish I could say I never found any issues but at least they are minor since I also run Adblock Plus and Ghostery as extensions in my browsers.
When I got my first mac I tried every anti-virus for macs on the market. Avast!, Bitdefender, Sophos, and Avira are the ones I remember. One at a time - not all at the same time ;P.
I finally figured out I did not need any of them. If I feel a fit a paranoia setting in I know I can run ClamXav so it can reaffirm for me that I really don't need any antivirus.
Lisa