Unlikely, but Mashable is throwing it out there (Update: Not happening):

It’s the second piece of information from our tipster that really piqued our interest, though. Leading the potential round will be Digital Sky Technologies (an existing investor) and Apple. Yes, Apple. The funding is part of a partnership between the two companies that will eventually result in deep Facebook integration into Apple’s suite of products, including Ping, iTunes, iLife and iWork.

Digital Sky is a somewhat shady Russian Venture capital group funded by Oliarchs that lists Goldman Sachs as part owners.  It would seem a bit out of character for Apple to participate in a funding round with Digital Sky.

Also, Microsoft owns 5% of Facebook so it would seem a little strange for both Apple and Microsoft to join in as owners.

That said, Steve Jobs is known to enjoy long walks with the Facebook founder, who is richer than Jobs, at least on paper. Apple would also like more Facebook integration into Ping and probably GameCenter as well.