To understand the dynamic mechanical properties and thermodynamic stability of β-Ti phase-embedded Zr/Ti-based bulk metallic glass composites (BMGCs), (Ti_0.474Zr_0.34Cu_0.06Be_0.126)_100-xFe_x (x=0, 2) BMGCs were prepared and investigated. Results show that by introducing Fe element, the stability of β-Ti phase is improved. An abnormal internal friction peak can be observed due to the precipitation of ω-Ti in the metastable β-Ti phase. Below the glass transition temperature T_g, both BMGCs show abnormal overshoot on storage modulus due to the coupling effect of phase transition and partial crystallization of amorphous matrix. This research provides information about the complex dynamic mechanical relaxation behavior of the in-situ metastable β-Ti BMGCs.