Probably you have an adware on your machine. Download and run AdwCleaner, reset settings in all your web-browsers, delete unused and suspicious browsers add-ons. I would suggest following the complete pop-up ads removal tutorial.
If you’re seeing unwanted pop-ups or ads, browser extensions or toolbars in your web-browser, you might have an adware, malware or spyware installed on your computer. Here are some steps you can take to remove unwanted software. Or ask for help here.