  Series of $I(V)$ characteristic and bias-dependent differential resistance
$dV/dI(V)$ for point-contacts on the single crystals of two-band superconductor
MgB$_2$ were measured in magnetic field up to 9 T. We have obtained magnetic
field dependences of the excess current on the $I(V)$ curves and analyzed them
using Koshelev and Golubov (Phys. Rev. Lett. {\bf 90}, 177002 (2003))
theoretical results for the mixed state of a dirty two-band superconductor.
Introducing a simple model for the excess current in the point contact in the
mixed state our data can be qualitatively described utilizing theoretical
magnetic filed behavior of the $\sigma$ and $\pi$-band superconducting order
parameters and the corresponding averaged electronic density of states in
MgB$_2$.
