  We report experimental observation of a new type of magnetic resonance caused
by orbital ordering in a strongly correlated electronic system. Cavity
measurements performed on CeB6 single crystals in a frequency range 60-100 GHz
show that a crossing of the phase boundary TQ(B) between the
antiferro-quadrupole and paramagnetic phases gives rise to development at T
<TQ(B) of a magnetic resonance. The observed mode is gapless and correspond to
g-factor 1.62.
