Linear magnetoresistance (LMR) observed in a topological insulator (Bi0.5Sb0.5)2Te3 thin film is systematically studied. LMR exists in very large ranges of temperature and magnetic field. It shows no trend toward saturation in the magnetic field of up to 18 T nor temperature dependence. LMR can be changed effectively by tuning the chemical potential through gate voltage. LMR shows a largest value when the chemical potential approaches to the Dirac point. These phenomena indicate that charge inhomogeneity is the origin of the LMR in this material.