Despite the accumulating evidence supporting an interaction between cognitive functions and postural control, little is known about the selective impact of the mental representation of an action, i.e., motor imagery (MI) on postural control. As postural oscillations are reduced during a cognitive task of backward silent counting, a greater stability is also expected during MI compared to a no-task condition (standing). Twenty participants took part in this experiment, which aimed at providing evidence that MI may improve postural stability. They were requested to mentally imagine a movement while standing on a force-plate. Results showed a decrease in both path length and postural sway variability on the anterior-posterior and lateral axes during all dual-task sessions, as compared to the motionless condition. These postural adjustments might result from both central and peripheral processes, and/or increased muscle stiffness. Conversely, postural oscillation amplitude increased on the vertical axis during MI of three vertical jumps, hence suggesting that postural regulations remain task-related during MI. Finally, our data showed that kinesthetic and visual imagery differentially impacted the postural regulation.