Answer: wind
Erosion is a natural phenomena, in which surface or subsurface soil is removed due to the action of agents like wind, water and others. In deserts sand is the only soil, which is found predominantly. The sand particles does not aggregate and highly porous in nature. The sand particles being lighter in weight are easily blown by the wind currents in the deserts, the phenomena associated with it is called as sand dunes.
Hence, the most common cause of erosion in deserts is wind.