The magnetic response of the Tb spins in Pb2Sr2TbCu3O7 to the applied magnetic field have been studied by ac susceptibility measurements. Both the in-phase component χ′ and the out-of-phase component χ″ of ac susceptibility are found to be sensitive to the frequency but not to the strength of the driving field. At high temperatures χ′ exhibits Curie-Weiss behavior, it departs from this behavior as the magnetic correlations between the Tb spins develop, and a cusp which is typical of antiferromagnetic ordering is clearly revealed at lower temperatures. The correlated Tb spins respond "better" to a driving magnetic field which has a lower frequency. The relative maximum of the dχ′ IdT versus T plot matches to the TN determined using neutron diffraction measurements. This relative maximum continues to occur at the same temperature as the frequency of the driving field is varied. It, however, shifts to a lower temperature as a dc external field is applied, indicating the antiferromagnetic coupling between the Tb spins are weaken by the dc field. Moreover, the thermal behavior of χ″ exhibits a well-defined peak around the transition temperature, and a dc field of strength 5 kOe smears the peak.