Dynamic mechanical relaxation is a fundamental tool to understand the mechanical and physical properties of viscoelastic materials like glasses. Mechanical spectroscopy shows that the high-entropy bulk metallic glass (La₃₀Ce₃₀Ni₁₀Al₂₀Co₁₀) exhibits a distinct β-relaxation feature. In the present research, dynamic mechanical analysis and thermal creep were performed using this bulk metallic glass material at a temperature domain around the β relaxation. The components of total strain, including ideal elastic strain, anelastic strain, and viscous-plastic strain, were analyzed based on the model of shear transformation zones (STZs). The stochastic activation of STZ contributes to the anelastic strain. When the temperature or external stress is high enough or the timescale is long enough, the interaction between STZs induces viscous-plastic strain. When all the spectrum of STZs is activated, the quasi-steady-state creep is achieved.