Two-dimensional (2D) magnetic materials are the focus of one of the most active areas of nano-materials research. However, most of them contain d electrons in the hosts or dopants which may lead to extrinsic magnetic behavior. Here we report a density functional study on the structural, electronic, and magnetic properties of an AlN monolayer (ML) doped with first-row atoms of X (X = Be, B, and C), which are free of d electrons. The calculations reveal that Be and C dopants, which substitute Al and N atoms respectively, can induce local spin moments, while B (for N) cannot lead to spin polarization in the AlN ML. More importantly, for Be doped AlN ML, a half-metallic ferromagnetism is observed, and the estimated Curie temperature is higher than room temperature. The long-range ferromagnetic coupling between doped Be atoms can be explained by a hole-mediated p–p interaction. Thus, our results provide a promising way toward 2D magnetic materials.