Is an antivirus really needed for Android?
You shouldn't need to worry about running an anti-virus on your phone. I would recommend running one on your PC though and having it set to scan peripheral devices. When you plug in your phone and it gets mounted as a mass storage device the desktop's antivirus will scan the phone for viruses' signatures and you will be doing the minimum to ensure your security. 

It is an illusion to believe that just because you are running *nix or OSX you won't benefit from the security afforded by AV software; that said you dont need to spend anything to get a good, lean program especially in Linux.