Mac Cleaner

Force Quit Safari ( command + option + esc keys).Then restart Safari holding the Shift key. If you still have problems Empty Caches (Safari menu > Preferences > Privacy > Remove all website data. (This will also remove history if you do not want to remove History open Safari Preferences > Advanced and check mark “Show Develop Menu” then choose “Empty Caches” from Develop Menu ).

Then go to Safari Preferences > Extensions and check there. If there is an extension delete it.

If the problem persists then download and run Malwarebytes. Malwarebytes will detect Advanced MacCleaner as PUP (Potentially Unwanted Program) and will remove the app and all of its components.

+2 for what macjack posted.

Safari – Popup takes over

Safari – Popup takes over (2)

Popup remover – Scam Zapper

Safari popups that won't go away

If the pop-up reloads, force quit Safari (command - option/alt - esc) and reopen with the shift key held down. If that doesn't work, disconnect from the Internet, go to Safari/History and delete the website. Quit and reopen with the shift key held down. Then reconnect to the Internet.

Safari -Tech support scam pop-ups

No, it is practically malware. No Anti-Virus software or so-called “cleaning” apps are needed or recommended for Mac OS. They can conflict with Mac's own built-in security. At best they will slow your Mac by using unnecessary resources and at worst will bork your entire system.

How to Remove Advanced Mac Cleaner Virus - ASC