Front end wobble when take hands off..?

[ozigoo]

I sometimes take my hands off the handlebars comming down a hill slowing down, and with my other bike never had any problems. Today I did it with the Honda for the first time and the handlebars started to wobble side to side after a few seconds, so I quickly grabed the bars again...This doesnt seem normal, any ideas...the tyres are pretty new, no uneven wear..maybe headstem bearings? Strange as the bikes only done about 20,000km...