The northeastern forest zone (NFZ) is a vital part of national strategic landscape of ecological security-Two Barriers and Three Belts of China, which has significant implications for carbon sink in global carbon balance. This study used net ecosystem production (NEP) as an indicator to evaluate carbon sequestration by forests in NFZ. Anselin Local Moran'I analysis was conducted to discern hotspots, coldspots, and outliers. The effects of natural and anthropogenic factors on carbon sequestration were explored by stepwise regression analysis and path analysis. Results indicated:(1) Overall, the forest ecosystem in NFZ acted as a carbon sink. The total amount of sequestrated carbon was 36.41 Tg C/a, with an average of 89.57 g C m^-2 a^-1. (2) Hotspots of NEP were mainly located in the northern part of the Daxing'an Mountains, the northern and central parts of the Changbai Mountains. Coldspots of NEP were mainly located in the eastern part of the Daxing'an Mountains, the Xiaoxing'an Mountains, and the southern part of the Changbai Mountains. Outliers of high NEP were mainly distributed in Agroforestry ecotones, while outliers of low NEP were mainly distributed in the areas of urban sprawl. (3) NEP of forest ecosystems in the northeastern forest zone positively correlated with NDVI; no significant relationships between anthropogenic factors and NEP were found. (4) Abnormally low values of NEP were primarily caused by anthropogenic factors (i.e., expansion of urban area). Simultaneously, a state of poor vegetation growth, as well as higher environmental temperature, could also prompt a decrease in carbon sequestration by forest patches.