Spontaneously formed temperature-frequency zone of negative dielectric permittivity ε′<0 was found in polymer-water system “poly(acylic acid)+3wt% of moisture”. Nucleation and evolution of the zone is demonstrated on ε′(f,T), ε″(f,T) and tgδ(f,T) 3D plots. Bound water release at T>65°C is thought to be the reason of this phenomenon. The frequency width of the zone steadily increases with temperature up to T=83°C, and then sharply increases at low-frequency side. This effect might be related to the anomalies in temperature dependencies of thermodepolarization currents in water at 83°C. Spontaneous manifestation of ε′<0 phenomenon indicates that one can expect it in natural materials, including biopolymers, i.e. in living organisms. •Dielectric properties of poly(acrylic acid) pressed pellets with different wt% of moisture were studied.•Temperature-frequency zones of negative dielectric permittivity were detected.•Bound water release at T>65°C is responsible for the phenomenon.