Is Linux safe from viruses?

Yes, if the question concerns the now and coming years. Virus writers tend to target Windows machines because of Microsoft's popularity and because of the operating system's inherently weak security mechanisms.

Linux fares much better because of its default security settings (secure repositories for software packages, stricter root/admin policies, etc.) and faster fixes.

However, as a general rule, no software is 100% insulated from viruses, even malwares and security breach codes. Linux may one day become as vulnerable as Windows, although, that may come in decades.

Meanwhile, read this interesting article (though a bit dated) comparing Windows from Linux in terms of security.