Firstly
Go directly to
www.PAYPAL.com in your web browser and see if there is such a pending charge.
Also on the email hover over the button and see what the URL is (should show it on the bottom left of the email program or as a mouseover pop-up) without clicking on it. Is it a true paypal domain?
If you click there's a chance that you'll end up at a non-paypal look-alike domain that will ask you for your username/password.
Thread title typo corrected