855-465-9466

This number appeared on what appears to be a false 'blue screen' that appeared with Windows warnings on a MAC computer.

I received the exact same thing as you!

This number appeared as part of a pop-up on my MAC with a voice saying I should call them, that my computer was infected and my financial info was at risk if I used my computer for shopping. That by calling the number I could fix the virus in my MAC. The pop-up and voice was persistence - I had to restart to get rid of it. I'm guessing it's a scam, but would like to know more.

Yes it is a scam. You have been the victim of scareware imbedded in an ad server on a website you recently visited.  Clear the safari cache and history and look into a 3rd party ad blocker for Safari.