It's a reasonable question, however an all clear from AV software may give you a warm feeling inside but doesn't guarantee anything. It is very difficult/impossible to achieve certainty as you normally end up having to trust some third party whether it be a hardware or software provider.
In as far as anecdotal evidence counts for anything I have used Ubuntu exclusively for more than 3 years without becoming aware of anything associated with malware (fraud, id theft, performance issues etc.). I looked into AV software, but what little I found focused on providing alerts for Windows malware (ie for scanning on linux prior to use on Windows).
For anyone starting out I would echo what other have said with regard to using a Live DVD/USB to try things out first.
Cheers SG
We were obviously posting at about the same time so in response I refer you to part of what I just posted to happypig:
"I don't pretend for a moment that any AV software guarantees 100% protection - as this is clearly not the case, but it's more a question of mitigating the risk. Because Linux is clearly more secure that Windows, does that mean that an extra layer of potential protection should be ignored?"
Also, a large part of my concern in this matter is on behalf of my friend who (although I'm no expert) is less savvy than me.
I'm getting a definite sense that NSC's Linux crew are firmly in the 'No AV required' camp though.
Yes, I certainly plan to run it 'live' before committing to an install.