It's not impossible for a Chromebook to get a viruse or malware, but it would be very unusual, for two reasons. Firstly 99% of malware targets Windows. Chromebooks run a version of Linux called Chrome OS. People who run Linux - I'm one - don't normally bother with antivirus programs. Secondly, Chrome OS is limited by design as to what it will run - essentally only Google apps. So you can't be tricked into loading a rogue app.

Because you use the Chrome browser it is possible to install a malware-infected extension from the Chrome Store. I think there are 'reset' options that will deal with that.