The dynamical behavior of carrier electrons varies from metals to insulators depending upon their intrinsic energy levels. The anomalous behavior of carriers in topological insulators makes it a prior candidate for numerous applications in the field of spintronics, optoelectronics, terahertz generation, and detection. This article reports the excited state dynamics of a thin shining flake of Bi2Se3 single crystal in which the kinetic profile is extensively analyzed. The ultrafast carrier dynamics of this crystal were studied over a wide NIR spectral range with several optical excitations using ultrafast transient reflectance spectroscopy. The thermalization of generated hot carriers due to the implication of pump beam and their relaxation pathways through different energy levels are predicted. The signal comprises optical (1–10 ps) and acoustic (10–50 ps) coherent phonon vibrations in the crystal. The FFD (filtering high-frequency component followed by fitting data) analysis is carried out to investigate the terahertz frequency generation dependence. This article has clearly shown the tunability of terahertz generation with external electromagnetic excitations and probe radiations.