Advancements in high-temperature thermoelectric (TE) materials have been substantial, yet identifying promising near-room-temperature candidates for efficient power generation from low-grade waste heat or TE cooling applications has become critical but proven exceedingly challenging. Bismuth oxyselenide (Bi$_2$O$_2$Se) emerges as an ideal candidate for near-room-temperature energy harvesting due to its low thermal conductivity, high carrier mobility and remarkable air-stability. In this study, the TE properties of few-layer Bi$_2$O$_2$Se over a wide temperature range (20–380 K) are investigated, where a charge transport mechanism transitioning from polar optical phonon to piezoelectric scattering at 140 K is observed. Moreover, the Seebeck coefficient (S) increases with temperature up to 280 K then stabilizes at ∼ −200 μV K$^{−1}$ through 380 K. Bi$_2$O$_2$Se demonstrates high mobility (450 cm 2 V$^{−1}$ s$^{−1}$) within the optimum power factor (PF) window, despite its T$^{−1.25}$ dependence. The high mobility compensates the minor reduction in carrier density n$_{2D}$ hence contributes to maintain a robust electrical conductivity ∼ 3 × 10$^4$ S m$^{−1}$. This results in a remarkable PF of 860 μW m$^{−1}$ K$^{−2}$ at 280 K without the necessity for gating (V$_g$ = 0 V), reflecting the innate performance of the as-grown material. These results underscore the considerable promise of Bi$_2$O$_2$Se for room temperature TE applications.