We know that the Cl-atom in chlorobenzene is attached to a sp2 hybridized carbon atom whereas, in cyclohexyl chloride, the Cl-atom is attached to a sp3 hybridized carbon atom. It is known that sp2 hybridized carbon has more s-character than sp3 hybridized carbon atom. Thus, chlorobenzene is more electronegative than cyclohexyl chloride.
Apart from this, the - R effect of the benzene ring of chlorobenzene results in decreasing the electron density of the C - Cl bond near the Cl-atom. And the C - Cl bond in chlorobenzene becomes less polar. Due to these reasons, the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.