I have a McAfee pop up that appears in my Safari browser. It's some sort of malware, I suspect. How can I get rid of it.

Start by reading Block pop-up ads and windows in Safari - Apple Support. If that does not adequately explain what you are encountering, a screenshot is likely to help. Please don't capture or upload any information that you may consider personal.

Instructions for capturing, editing (if necessary) and posting a screenshot to this site can be found in the Appendix in Writing an effective Apple Support Communities Question - Apple Community. Scroll down to Screenshots (Mac).

You may be encountering a Safari Notification. Refer to this excerpt from Effective defenses against malware and other threats - Apple Community — specifically, the last bullet point below:

Beware spontaneously appearing, unsolicited popups demanding immediate action. Think before you click.

• Popup windows are useful and required for some websites, but unsolicited popups are commonly used to deceive people into installing unwanted software they would never intentionally install.
• Ad-blocking Safari Extensions can help, but none are completely effective, and all of them can cause unexpected behavior.
• If you encounter a website, popup, text message, email, or phone call alleging your Mac is infested with some ick or that you need to take immediate action lest dire circumstances ensue, it is 100% fraudulent. Ignore it. Read Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams.
• The same goes for website Notifications — attention-getting banners that appear at the top right corner of your screen. Safari gives you a great degree of control over them: Customize website notifications in Safari on Mac. Most of those Notifications are simply annoying, but some are intended to frighten and deceive you into installing something nefarious.

If that describes it, the reason it happened was that you agreed to have a website send you Notifications. Unless you have a valid reason for agreeing to that annoyance, your automatic and reflexive response ought to be "just say no."