Have you changed anything recently or done any work on the bike or did this just start happening out of the blue?
Also, is it stock or are you running an aftermarket ignition?
Does it sputter and backfire while sitting still and revving it or only under load while driving?
Tell us a little more about how and when it started behaving like this and hopefully it'll help point you in a more specific area to check as well. If it's coming out of winter storage with stale fuel the diagnosis will be different than if it was running perfect and "I washed it and it started running funny". ;-)