The single most important thing to do is to practice a little discipline while installing new programs or downloading files from the internet, including seemingly harmless files like images. Special caution for email attachments.
With that said, and bearing in mind that no system is absolutely impenetrable, Linux generally does not need an antivirus. There are utilities to scan files for known malware signatures like ClamTK as mentioned above. Here's a couple of threads that talk about this issue, the second one is my own approach to this.
This threads also have important details so try to give them a read if you can.