When asked if Rage 2 was being planned, Carmack answered with a flat "Yes," adding, "We haven't got a formal, official announcement, but we're certainly headed in that direction."
That said, don't expect Rage 2 anytime soon. Carmack said that as soon as Rage goes gold, id's core engineering team--led by Carmack--will transfer over to the Doom 4 team to shepherd it to market. Once that is completed, they will turn their attention to the next Rage game.
http://e3.gamespot.com/story/6318338/e3-2011-rage-2-already-planned-possibly-cross-generational