It would be unusual and, I suspect, would be counter to the design intent of the typical business card, in which information is visually separated out so that it is easily located. Using a semi-colon to separate a URL and an e-mail address might, however briefly, make both bits of information less than perfectly clear. If you're looking for an e-mail address on a card, you are unlikely to look at the end of what seems to be something else. It would be better to separate out the two pieces of information with a healthy space between them, or by putting them on separate lines.

I would also try to stay away from using a semi-colon on a buisness card, using the space that is available on the card would mean you would not need to use any colons.
Using slightly different type weights helps to make a clear seperation between two words or addresses such as email address and website address.