  The chalcogenide Bi$_2$Se$_3$ can attain the three dimensional (3D) Dirac
semimetal state under the influence of strain and microstrain. Here we report
the presnece of large linear magnetoresistance in such a Bi$_2$Se$_3$ crystal.
The magnetoresistance has quadratic form at low fields which crossovers to
linear above 4 T. The temperature dependence of magnetoresistance scales with
carrier mobility and the crossover field scales with inverse of mobility. Our
analysis suggest that the linear magnetoresistance in our system has a
classical origin and arises from the scattering of high mobility 3D Dirac
electrons from crystalline inhomogeneities. We observe that the charged
selenium vacancies are strongly screened by high mobility Dirac electrons and
the neutral crystalline defects are the main scattering center for transport
mechanism. Our analysis suggests that both the resistivity and the
magnetoresistance have their origin in scattering of charge carriers from
neutral defects.
