I haven't heard many people saying that Mac's gets viruses. I've however heard many people saying that the Mac users shouldn't be to confident there won't come viruses to Mac OS X.
Which is true, never say never. But there is no *virus* for the Mac at the moment.
There's however a couple of trojans, illegal copies of for example iWork '09 or Photoshop CS4 has been reported to contain trojans.
https://www.macrumors.com/2009/01/22/iwork-09-torrent-carrying-os-x-trojan/
Keep in mind that to be infected by such malicious application one must enter his/hers administrator password to allow the installation.
Keep away from untrusted sources and think twice before entering your password when installing things and you should be fine.