In everyday life, we are constantly making decision on our future actions, often under dynamic and uncertain conditions. In this study, we investigated how different sources and levels of decision uncertainty affect movement execution in goal-directed reaching movements. In addition to replicating early findings on the distinct effect of different levels of target uncertainty on movement execution, we were able to show, for the first time, that also the source of target uncertainty has a significant influence on movement execution, by analyzing the time course of movement variability.