A question a lot of people would like answered without equivocation!
When I bought my first Mac about two and a half years ago ago I asked much the same question, and the answer here was generally cautious in that nobody wanted to be irresponsible by saying there was absolutely no need for antivirus programs. But nobody bothered recommending one and my Apple stockist didn't sell any.
Furthermore, a Google search for anti virus programs for Macs came up with virtually nothing except some desperate posturing from the major av companies who warned wildly against complacency and urged me to send them a hundred bucks. I resisted the temptation.
Warnings were and still are frequent that the increasing numbers of Macs being sold means virus producers will any day now divert their attention away from Windows because it is becoming worth their while (as though there is money to be made in inventing viruses rather than programs to eliminate them). We still appear to be waiting for that day to arrive.
Greater minds than mine will update you on the current risk I am sure, but my local Apple store still doesn't sell any AV programs, I have an iMac and a MacBook and am about to buy another macBook, I've never had an AVprogram installed and until solid advice arrives to the contrary I don't intend getting any.
Of course if you are going to install Windows on your Mac for whatever reason, disregard all of the previous advice.
Good luck with your Mac!