Virus alert popped up, looks exactly like Apple page. Is it a scam?

As Terence has said, it is a very convincing scam hoping to panic you into action. You may see this scam in an email too. Your first clue is that there are no viruses on a Mac; that no web site could check your Mac anyway, and of course, the real Apple will never interject junk like this in Safari, or from the operating system itself. Don't revisit that web site where this crap appeared.

Provided that you are using Safari, select the Safari menu, and choose Clear History… all history and click the Clear History button. Once you have done that, just quit Safari (⌘-Q). Next, press and hold the shift key while you relaunch Safari. Repeat the Clear History process, as with Safari 12 or later, this will also clear the cookies from your browser cache. Quit Safari again, and then relaunch.

As further precaution, you may wish to download and run Malwarebytes which will check your Mac for malware (not viruses). If it finds any, it will inform you, and allow for their removal. I, as well as many of your fellow users here use Malwarebytes ourselves. Any subscription mentioned is purely optional, and I personally to not have a subscription.

Please do not fall for the convincing marketing for Mac anti-virus products, and so-called cleaner products. These will do more harm than good when installed on Macs and it is a constant issue in these support communities.

It's a scam. Ignore it.

It's ALWAYS a Scam.