The dynamics of Davydov-Scott monomer in a thermal bath with higher order amide-site's displacement leads to anharmonic oscillation effect is investigated using full-quantum approach and the Lindblad formulation of master equation. The specific heat is calculated based on the thermodynamic partition function using the path integral method. The temperature dependence of the specific heat is studied. In the model the specific heat anomaly as pointed out in recent works by Ingold [Phys. Rev. E 79, 061105 (2009)] is also observed. However, it is found that the anomaly occurs at high-temperature region, and the anharmonic oscillation restores the positivity of specific heat.