Rabid Macolytes will insist no antivirus is required - and that's an argument that has no end - but given that I trade documents and information with others who may not be on Macs, I am of a view that I don't necessarily want to transfer someone else's problem - if not to my Mac - to another's computer inadvertently. As well, as Macs have increased in popularity (as well as the variety of different browsers that now work on Macs), there is more 'value' and opportunity to those who build viruses, malware, keyloggers, etc to do so.
I finally came full time to Mac when Win8 was released - and with it, I brought my paranoia about viruses and malware. I was using the free Avira AV on my Win machine and they have a Mac version, too. Its not in the Mac App Store, so do a Google if interested. It has all sorts of manual controls, the ability to set scheduled scans and updates, etc, etc. I've not had a problem with it. And I have no problem with the price!
There are a number of other AV products in the App Store (which suggests that even Apple may not agree with its biggest fans) - BitDefender and Trend Micro two familiar brands - but I've no practical experience with either.
Hope this helps.