The mechanical loss (Q(-1)) and shear modulus (G) were measured as a function of temperature in the range 130 K < T < 430 K for BaTiO3 ceramics by an inverted pendulum at low frequencies ranging between 1-0.01 Hz. The Q(-1) (T) and G(T) curves exhibit the three phase transitions observed in BaTiO3. Each phase transition induces a loss peak and an anomaly in the elastic modulus. Moreover, three other loss peaks (R) are located below the phase transition temperature. These peaks can be described by an Arrhenius relationship, and the activation energies are determined as 0.92, 0.68, and 0.45 eV for the peak located in the tetragonal-, orthorhombic-, and rhombohedral-phase, respectively. These peaks are due to the interaction between the domain walls and the diffusion of oxygen vacancies in the domains.