In this work, we employed angle resolved photoemission spectroscopy (ARPES) to analyze the temperature dependent changes in the electronic structure of the first antiferromagnetic topological insulator MnBi ₂Te ₄ upon crossing the Néel temperature T _N ≈ 25 K. We observed an exchange splitting of the bulk conduction band, which has a power law dependence on temperature (1-T/T0)2β with an onset temperature T ₀ well matching the measured bulk T _N. We found a matching temperature evolution of the topological surface states integrated spectral weight in the vicinity of the Dirac point. Furthermore, we observed an additional quasi-2D state with Rashba-type splitting, which is also affected by the emerged magnetism and exhibits an opening of a gap, reminiscent of the effect of an out-of-plane magnetic field, below T _N. All these findings point toward strong evidence of the interplay between emerged magnetism with bulk and topological surface states. The observed temperature-dependent effects in MnBi ₂Te ₄ may be used as an experimental fingerprint for the presence of magnetism and may guide the future analysis of ARPES spectra in magnetic topological insulators.