The complex dielectric response of tungsten bronze Sr1-xBaxNb2O6 (SBN (1-χ)/χ,χ"0.40, 0.50, and 0.60) relaxor ferroelectric ceramics has been carefully studied as a function of temperature between-180 and 450℃. Three distinct relaxation features were observed in all the compositions. The thermal hysteresis of dielectric maximum was considered to be associated with "lock in" of the incommensurate phase. It was confirmed by investigation of the Curie-Weiss behaviour in the higher temperature range. In addition, it was found that the weakness of the dielectric dispersion below the ferroelectric-paraelectric phase transition temperature can be induced by ageing and poling. These results are discussed in terms of the polarization fluctuation and metastability of polar microregions.