NO OS is immune from malware, though there is less malware in the wild targeted at Linux. But there IS some out there, and you would be wise to keep that in mind for your surfing and email habits.
Indeed, Linux has some good command line rootkit detectors (can't remember what they are right now, but I think they are both in the main repository.)
Now I said there are not many Linux viruses in the wild, and there aren't. BUT, that's not necessarily because of Linux's security. The main reason there aren't is simply because of market share. Windows has over a 90% market share, therefore the malware writers get the biggest bang for their buck by targeting Windows.
As Linux gains more users, the malware situation for Linux will worsen.
Some Ubuntu people, especially some "experienced users" on the Ubuntu forums, are particularly arrogant, smug, pedantic, and OBNOXIOUS when you ask them about an antivirus. The typical answer might be "Linux is immune and you are foolish if you think you need an antivirus."
I have cautioned some of those folks to "Watch out what you're wishing for . . . you may get things you haven't planned for." What I meant was that since they are Ubuntu fanboys and want to see Ubuntu increase their market share, the malware writers, who get the biggest bang for their buck targeting the 800 pound gorilla, may just see a good target if Ubuntu users increase.
Might be better to continue flying under the radar and remain a poor target rather than show increasing usage and become a good target.
The MAC guys found out about infections and Apple being "IMMUNE".
Now I'm not bashing the Ubuntu forums. On the contrary, I do get some good advice on there. But be aware that if you ask your question about a Linux antivirus on those forums, you're likely to get some condescending and negative answers.
Noobs that take some of that stuff without question can get a bum steer.
But Rick is correct when he says the "General opinion". It just happens that as a Linux user I disagree with that "General Opinion." But then I'm a security freak and I HAVE seen infected Linux systems. Rare? Yes, but they DO exist.
So, my answer (to your three month old question . . . sorry, I might be a little late here but I don't visit HTG that much anymore) is YES . . . you would be wise to run an antivirus scan at least once a month . . . more often might be better too.
If you follow best security practices and watch your surfing and email habits, your antivirus program will likely be like a Maytag Repairman . . . nothing to do.
But for that rare time that you might get infected no matter what you do (and that DOES happen . . . there's no such thing as 100% foolproof security), an antivirus program can be a lifesaver. I run Avast.
"Sky is falling" thinking? Perhaps. Paranoid? Maybe. But have I reduced my risk by running an antivirus program . . . even in Linux? Yes.
(BTW, I have Frontier DSL and connect via wireless too. Tip: If you ever change your ISP password, call and tell Frontier right away. If the password they have on file for you doesn't match what's in your router, you won't be passed through to the Internet. Your machine indicator will show a connection, but that will only be between your machine and the router. Your DSL, WIreless, and Power lights will be green on your router, but the Internet light on your router will be red in that circumstance.)