  We report electronic transport measurements on single crystals of
NaFe$_{1-x}$Co$_x$As system. We found that the cotangent of Hall angle,
cot$\theta_{\rm H}$, follows $T^4$ for the parent compound with filamentary
superconductivity and $T^2$ for the heavily-overdoped non-superconducting
sample. While it exhibits approximately $T^3$-dependence in all the
superconducting samples, suggesting this behaivor is associated with bulk
superconductivity in ferropnictides. A deviation develops below a
characteristic temperature $T^*$ well above the structural and superconducting
transitions, accompanied by a departure from power-law temperature dependence
in resistivity. The doping dependence of $T^*$ resembles the crossover line of
pseudogap phase in cuprates.
