Not unless you plan on downloading and installing a bunch of random unverified and untrusted applications.
Macs ship in stealth mode, so essentially the only way to contract a virus on a Mac is to download and install the file yourself, which no anti-virus could prevent.
Your best bet is to research and verify any apps you want to install and make sure you are obtaining legal copies from trusted sources.
The general consensus among users here is similar to the previous post. None necessary at this time.
There are certain exceptions, such as a employment environment that requires an AV from all users of a network. In this case, ClamAV seems to suffice without impacting the Mac experience significantly.
I have never run an AV on any of my OS X Macs, and have never had a problem. And with my browsing activity, I'd be "toast" if I used a Windows system in a similar manner, even with a Windows AV. That shows just how relatively safe a Mac is from malware attack.
I would advise you to become familiar with your operating system, particularly the manner in which any official notifications are made. This is so you don't fall victim to any cyber attacks that trick you into installing a piece of software that masquerades itself as some sort of unsolicited system update or addendum. As of late, that has been about the only vulnerability.