One should have AV on any smart phone as it is, in affect, a small computer. They often come with that app already installed; no idea if the Galaxy does though. I suspect you might get away with taking the risk, at you own risk of course.
If you use it to access the Net then maybe, but unlikely. A mobile phone virus tends to either stop the phone working (for a laugh) or, I would suspect, sit there unnoticed gathering information, or maybe dialing out premium numbers perhaps ? I suppose a badly written one might cause issues, but it's more likely a hardware fault IMO.