I just got a pop up from 'Apple Care' telling me I have the trojan virus. Is this a scam

Yes and a poorly crafted one. There are no known viruses for Mac OS and besides that no one can know what is on your Mac. Force quit Safari holding the command-option-esc keys and then restart holding the Shift key. Do not revisit the same website that generated it.

If the above doesn't work, you may  have adware/malware installed. Try downloading this program which was written by Thomas R, a long time poster. The program will search for malware/adware. The program will do the work for you which makes it easy. It may be necessary to run more than one scan. After running the scans, restart the computer.

Malwarebytes Anti-Malware for Mac      10.10 and later

Malwarebytes uninstall

I also received this pop-up telling me my Mac was infected, however, I was working on my iPad. Also, I was accessing, what I thought was the Encyclopaedia Britannica website (https://www.britannica.com/biography/Saint-Paul-the- Apostle) after doing a search in Safari. FYI.