FeGa3 has attracted considerable attention as potential material for many fields, whereas the whiskering phenomenon may cast doubts on its applications. Spontaneous Ga whisker formation was observed on the ballmilled FeGa3-Ga. The sample made from ball-milled FeGa3 powders free of elemental Ga are immune to the Ga whisker formation, even if all the processing parameters were the same as the FeGa3-Ga composite sample. In addition, several nano-sized Ga whiskers were found on the pressed FeGa3-Ga composite without ball milling, and the as-synthesized FeGa3-Ga grew only tiny Ga balls on the surface. These whiskering phenomena do not follow the traditional metal whisker formation mechanisms. A newly proposed catalysis-based mechanism, in which the cleavage planes of FeGa3 grains act as heterogeneous nucleation sites and the elemental Ga provides Ga atoms for whisker formation, is employed to explain Ga whisker formation on FeGa3.