  We report the magnetic field dependence of resistivity ($\rho$) and specific
heat ($C$) for the non-superconducting PrFeAsO compound. Our study shows a
hitherto unobserved anomaly at $T_{SR}$ in the resistivity and specific heat
data which arises as a result of the interplay of antiferromagnetic (AFM) Pr
and Fe sublattices. Below the AFM transition temperature ($T_N^{\rm{Pr}}$), Pr
moment orders along the crystallographic c axis and its effect on the iron
subsystem causes a reorientation of the ordered inplane Fe moments in a
direction out of the $ab$ plane. Application of magnetic field introduces
disorder in the AFM Pr sublattice, which, in turn, reduces the out-of-plane
Pr-Fe exchange interaction responsible for Fe spin reorientation. Both in
$\rho$($T$) and $d(C/T)/dT$ curves, the peak at $T_{SR}$ broadens with the
increase of $H$ due to the introduction of the disorder in the AFM Pr
sublattice by magnetic field. In $\rho$($T$) curve, the peak shifts towards
lower temperature with $H$ and disappears above 6 T while in $d(C/T)/dT$ curve
the peak remains visible up to 14 T. The broadening of the anomaly at
$T_N^{\rm{Pr}}$ in $C(T)$ with increasing $H$ further confirms that magnetic
field induces disorder in the AFM Pr sublattice.
