Bungie has not made a PC game since 2001. However, news coming out of the BMO Digital Entertainment Conference seems to suggest that Bungie is indeed developing a title for all platforms, both PC and console, and that it will be online.
A presentation slide from Activision at said conference has apparently confirmed that Bungie’s first game for the publisher will be an online game for both PC and consoles.
If this is indeed true, the game will be Bungie’s first PC game since Oni (2001) The PC ports of Halo and Halo 2 don’t count. :-)