  We report observation of substantial thermal relaxation in single crystal of
charge ordered system Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ in an applied magnetic
field of H = 8T. The relaxation is observed when the temperature is scanned in
presence of a magnetic field in the temperature interval $T_{MH}<T<T_{CO}$
where $T_{CO}$ is the charge ordering temperature and $T_{MH}$ is charge
melting temperature in a field. In this temperature range the system has
coexisting charged ordered insulator (COI) and ferromagnetic metallic (FMM)
phases. No such relaxation is observed in the COI state in H = 0T or in the FMM
phase at $T < T_{MH}$ in presence of a magnetic field. We conclude that the
thermal relaxation is due to two coexisting phases with nearly same free
energies but separated by a potential barrier. This barrier makes the
transformation from one phase to the other time-dependent in the scale of the
specific heat experiment and gives rise to the thermal relaxation.
