A cooling air filter for an electric motor, includes a filter with a planar shape and minimum dimension so as to cover the area of the slits of a covering casing of a fan for an electric motor for which it is intended; and the filter is housed in a support which is fixed in a steady and removable way on the surface of the casing; the support having a frame-like structure from which at least two arms extend, which are diametrically opposite in the frame-like structure, and which are provided at their end with fixing and gripping means of the arms on the casing itself; the fixing means being configured for the fast detachment from and hooking onto said casing.