We have studied the effect of spin-orbital coupling (SOC) on the electronic transport properties of the thermoelectric material β-K₂Bi₈Se₁₃ via magnetoresistance measurements. We found that the strong SOC in this material results in the weak antilocalization (WAL) effect, which can be described well by a three-dimensional weak localization model. The phase coherence length extracted from theoretical fitting exhibits a power-law temperature dependence, with an exponent around 2.1, indicating that the electron dephasing is governed by electron-transverse phonon interactions. As in topological insulators, the WAL effect in β-K₂Bi₈Se₁₃ can be quenched by magnetic impurities (Mn) but is robust against non-magnetic impurities (Te). Although our magnetotransport studies provide no evidence for topological surface states, our analyses suggest that SOC plays an important role in determining the thermoelectric properties of β-K₂Bi₈Se₁₃.