(or lord sorry in advance for the long reply, ngl i have a terrible problem with these kinds of things and i've been trying to do better and sometimes you notice it in some replies i send, but other times, like this, it still is really, REALLY bad)
Now, i do want to say first and for most, yes, these are scams, fake, not real, don't worry, types of things, and most importantly, we all get them, not just you, BUT if you are getting them abnormally often and/or you're getting them on websites that shouldn't do this (examples, youtube.com, yahoo.com, apple.com, microsoft.com, etc), you can download an antivirus and see if your computer has a virus like adware, i personally don't think this is the case and its just simply maybe you going to random websites that aren't secure or are hijacked, but if you think you do have adware (which again, i highly doubt, especially considering this is actually decently common) i'd suggest either downloading malwarebytes at https://www.malwarebytes.com/mac/ and clicking "free download" in the top right, and/or you can get something that'd do a deeper scan called bitdefender on the app store at https://apps.apple.com/us/app/bitdefender-virus-scanner/id500154009?mt=12, honestly i personally use malwarebytes only but i have had a case where my grandma's MacBook Air was so messed up that i had to download both malwarebytes and bitdefender, but in most cases your perfectly fine with malwarebytes.
so again, i really doubt its adware but if you personally think it is, then here you go, but honestly we all get it (random pop ups like that), i'm only saying this as an option because you claim its happening when you open a website (which sounds a bit broad) and you also say that its happening quite frequently, so i just thought i'd say this as an option because while yes, this does happen a lot and is quite harmless, it shouldn't, under normal circumstances, happen TOO too much and only really happens when you go to a not so great website or something, i hope this helps and either goes away on its own, gets fixed with one of those programs, or gets ruled out as normal (which is honestly very likely considering they look like the normal fake virus pop up) and if you have any other questions, comments, concerns, literally anything, feel free to ask/say and i or someone else would love to help further (so basically in my opinion i really don't think this is something you should be worried about but if you think it is adware, like i said, you can and should give it a shot, but its 100% up to you)