Hi Mary, this is a tech support scam - don't call the number. Most commonly such pop-ups are caused by deceptive ads in various not so great websites. In such case it's enough to end the process of your Internet browser or just restarting your computer. In other cases such pop-ups are caused by adware. If you constantly see such scam pop-ups you should scan your computer with Spyhunter, Malwarebytes Antimalware and AdwCleaner (https://toolslib.net/downloads/viewdownload/1-adwcleaner/). These programs are great at detecting and removing adware that cause such unwanted pop-up ads.