virus scan?

It'll be something other than a virus that's causing the problem. It could perhaps be caused by incompatible software. Can you describe how often it happens, if it's only when performing certain tasks, how long does the freeze last, does it 'unfreeze' itself or do you have to restart, etc.

You may want to download and run the free EtreCheck and post the contents of its report on here. I'm not expert on spotting what may cause the problem, but plenty here are. That said, there is some software that is known to cause Macs to perform oddly so it may be obvious.

http://www.etresoft.com/etrecheck

I agree with Paul, this isn't being caused by malware.

When you say your screen is freezing, what does that mean? Is your computer completely freezing up, requiring a forced shutdown? Is there any kind of message, such as an alert in multiple languages telling you that you need to restart? Or is it a temporary thing, where things seem to freeze up for a moment and then everything starts working again? Does it seem to be specific to a particular app (ie, other apps are working fine when it freezes)?