The magnetic ground state of Sr2CrO4 with a distorted honeycomb lattice was investigated by means of measurements of the magnetic susceptibility, high-field magnetization process, and electron spin resonance (ESR). Antiferromagnetic ordering was observed clearly below TN = 3.2 K, while the magnetic ground state had been thought to be a spin-singlet state. A two-sublattice model with biaxial anisotropy was applicable for the observed ESR modes. Plateau-like behavior and a sharp kink were detected in the magnetization curve.