Malware Pop-Up

I am receiving a pop-up stating "Mac is full of Virus, click to remove virus" also "Mac camera is controlled?" or hacked and this is not only on websites. It is on startup as well. I had downloaded Malwarebytes and it could not find any malware on the device. Yet, the popups still exist beyond just browsing the web. Any other pointers as to how to fix this? It's been persistent for the past month since mid-Janurary when I got my laptop back from a friend. This is a frequent occurance every 2-5 minutes it pops up.