A mechanism is proposed for the self-sustainment of a magnetic turbulence resulting from an equilibrium between islands and a chaotic region in a collisionless plasma. It is based on the different behaviour of electrons and ions in the presence of the islands as a result of their different Larmor radii. This effect leads to a difference in their drift velocities and hence to a current which maintains the islands. The mechanism operates for island width smaller than or comparable to the ion Larmor radius. The condition for the self-sustainment of the magnetic turbulence is derived.