  We have studied the vortex dynamics in the PrFeAsO$_{0.60}$F$_{0.12}$
superconducting sample by dc magnetization and dynamic magnetization-relaxation
rate $(Q)$ measurements. The field dependence of the superconducting
irreversible magnetization $M_s$ reveals a second magnetization peak or
fishtail effect. The large value of $Q$ is an indication of moderate vortex
motion and relatively weak pinning energy. Data analysis based on the
generalized inversion scheme suggests that the vortex dynamics can be described
by the collective pinning model. The temperature dependence of the critical
current is consistent with the pinning due to the spatial variation in the mean
free path near a lattice defect ($\delta l$ pinning). The temperature and field
dependence of $Q$ indicates a crossover from elastic to plastic vortex creep
with increasing temperature and magnetic field. Finally, we have constructed
the vortex phase diagram based on the present data.
