It's headshake (as stated above). Easiest fixes are to run more sag out back, lower your forks in your triple clamps or tighten your steering nut. Best fix is to get your suspension sorted out and add a steering damper.
The Scotts damper is $350 US, plus you need a mounting kit. Talk to BRP (www.brpit.com), they can set you up with one. I got a Scotts damper, top triple clamp, SUB mount, and bolt on post for $620 USD. I'm extremely happy with my setup and can't imagine riding without one now.