Answer: You May Have A Virus
So I hate to be the bearer of bad news here, but you most likely are the victim of a malware attack. One of the most common manifestations of malware is them actually taking the form of a “antivirus” pop-up that scares you into purchasing a fake program to “delete” the malware only to be victimized again in the future.
Of course, if you happen to get a pop-up every once in a while, or get some spam in your email, then there’s nothing to worry about. But if you’re getting these popups every website you visit, especially reputable ones like Google.com or Wikipedia, you need to properly clean your computer. I would suggest sending it to a reputable PC repair technician. At Cellar Door, we offer these services but there are many other technicians too.