We report results of DC-magnetization and 1 1 B-NMR measurements on single crystalline YbB 6 . The magnetization data at temperatures between 4 and 300K reveal weak ferromagnetic order with a T C >300K. It involves very small ordered moments, of the order of 0.002μ B /f.u., representing only a small fraction of the effective paramagnetic moment per formula unit that is indicated by the magnetic susceptibility. The latter can be accounted for by assuming that 2% of all the Yb atoms adopt the Yb + 3 configuration. Since almost all the Yb ions adopt the divalent configuration one expects YbB 6 to be a poor metal.