Dielectric relaxation behaviour of the guest-host mixture of a ferroelectric side chain liquid crystalline polymer (FLCP) and a nonlinear optical (NLO) dye has been investigated with broadband dielectric relaxation spectroscopy. The liquid crystal (LC) phases of these guest-host materials were characterized with the differential scanning calorimeter, optical polarizing microscopy, and X-ray diffractometer. No phase separation is observed when the doping level of the NLO dye is below 10wt%. The doping of the NLO dye into the FLCP results in the significant increase of the relaxation intensity and frequency of the Goldstone mode in the chiral smectic C phase (S-C*) Moreover, the NLO dye has high relaxation intensity in the LC phase for such guest-host material. On the other hand, the occurrence of phase separation is observed when the doping level of the NLO dye is 30% by weight. The phase separation results in the reduction of the relaxation intensity for both the Goldstone mode of the FLCP and molecular motion of the NLO dye. The relationship between the thermal dynamic behaviour and the environment around molecules for such NLO active guest-host material was discussed in great detail.