  Having taken the QED radiative correction and one-loop weak corrections into
account, we have computed the unpolarized forward-backward asymmetry in the
process $e^+e^- -> \mu^+\mu^-$ at a very reasonable accuracy. Special attention
to the effects around the LEP 200 energy, induced by the possible $Z'$ boson of
the left-right symmetric model $SU(2)_{L} \times SU(2)_{R} \times U(1)_{B-L}$,
is paid. The numerical results of the directly measurable asymmetry
$A_{FB}^{\mu}$ versus the CMS energies are presented in figures. One may be
convinced by the results that precise measurements on the asymmetry in future
colliders will possibly present some indirectly evidence of the $Z'$ boson.
