  We use inelastic neutron scattering to study the crystalline electric field
(CEF) excitations of Ce$^{3+}$ in CeFeAsO$_{1-x}$F$_{x}$($x=0,0.16$). For
nonsuperconducting CeFeAsO, the Ce CEF levels have three magnetic doublets in
the paramagnetic state, but these doublets split into six singlets when Fe ions
order antiferromagnetically. For superconducting CeFeAsO$_{0.84}$F$_{0.16}$
($T_c=41$ K), where the static AF order is suppressed, the Ce CEF levels have
three magnetic doublets at $\hbar\omega=0,18.7,58.4$ meV at all temperatures.
Careful measurements of the intrinsic linewidth $\Gamma$ and the peak position
of the 18.7 meV mode reveal clear anomaly at $T_c$, consistent with a strong
enhancement of local magnetic susceptibility $\chi^{\prime\prime}(\hbar\omega)$
below $T_c$. These results suggest that CEF excitations in the rare-earth
oxypnictides can be used as a probe of spin dynamics in the nearby FeAs planes.
