Weird pop-ups are basically almost always going to be mal-ware, unless you've got some sketchy program that you use normally (hi2U AVG) that just likes to spam you with BS.
But if the pop up is there, you can usually use the task manager to figure out what it is, and use that to trace it to where it's installed, if you're not willing to DL more software.
But I'd definitely recommend also going through your program list and looking for stuff that you don't use/think should be there and uninstalling it, and being more careful about what you DL in the future.
