  The active-sterile neutrino conversion is studied for neutrino propagating in
the axial potential generated by magnetised electron plasma in the supernova
medium. We consider the effect of random magnetic field $B_{rms}$ on the
average neutrino conversion probability. We obtained the constraint on $\Delta
m^2$ and $\sin^2 2\theta$ for different strength of the random magnetic fields,
by considering the positive definiteness of the average neutrino conversion
probability inside the supernova core. Our calculation shows that, $B_{rms}\le
0.63\times 10^{14}$ Gauss is preferable so that small values of $\Delta m^2$
can not be excluded.
