can you feel the bike wobblingas you ride, or just see it? If you can feel it then the cause is probably a damaged tire... if the wobble is all in the rim and spokes it is often very hard to feel even if it is easy to see. If it is the tire, the damage is often caused by a brake pad rubbing on the tire. Sometimes the tire will wear thru and blow out instantly and sometimes it will be ridable for some time before blowing. Either way you need to replace the tire and adjust your brake pads.

If you can not feel the wobble when riding but it is obvious when you look at it, then you likely have one or more broken spokes - usually this happens on the drive (chain) side after a new bike has been ridden a few hundred miles... and is usually the result of an improperly built wheel.