If it is the Avast! Network Shield doing this, you have something on your system that is trying to connect to a url that Avast! has blacklisted (usually for good reason) so it is either a program you have knowingly installed doing this, or you have an underlying infection like a trojan downloader (and possibly an accompanying rootkit).
You could probably mess with the registry to disable the pop-ups, but I won't help you with that any more than I would help someone with AIDS find a one-night stand. Run a scan with something like Malwarebytes, maybe also an Avast! boot-scan......you might be surprised.