Novel topological phenomena are anticipated for three-dimensional (3D) Dirac electrons. The magnetotransport properties of cubic Sr3PbO antiperovskite, theoretically proposed to be a 3D massive Dirac electron system, are studied. The measurements of Shubnikov–de Haas oscillations and Hall resistivity indicate the presence of a low density (∼1×1018cm−3) of holes with an extremely small cyclotron mass of 0.01–0.06me. The magnetoresistance Δρxx(B) is linear in magnetic field B with the magnitude independent of temperature. These results are fully consistent with the presence of 3D massive Dirac electrons in Sr3PbO. The chemical flexibility of the antiperovskites and our findings in the family member Sr3PbO point to their potential as a model system in which to explore exotic topological phases.