if your brakes are ok (calipers, sliders, brake pads) this can happen if the pads are not good quality or if small pieces of rocks make it between the pads and the disks (like really tiny bits that can fit in there) - would go away after a while in this case. So if you offroad often on dusty roads that can be the cause in which case there's not much you can do, in the first case get a good quality set of pads.