Magnetic bioactive glass–ceramic (MBGC) with bioactivity and a self-heating ability under an alternating magnetic field (AMF) is specially designed to treat bone defects resulting from tumor resection, thereby preventing tumor recurrence and regenerating the damaged bone. In this study, to enhance the self-heating ability of MBGC, magnetic Fe3O4/bioactive glass–ceramic (CaO-SiO2-P2O5-MgO) scaffolds were prepared using graphite-modified precursors and by completely covering the raw materials in graphite during the calcination process. The results show that graphite can prevent the oxidation of Fe3O4 in the scaffold, which gives the material good magnetic and magnetothermal properties. Under a magnetic field of 1 × 106 A·m−1, the saturation magnetization and coercivity of the scaffold were 18.2 A·m2·kg−1 and 4.9 × 102 A·m−1, respectively. Furthermore, when exposed to AMF (340 kHz, 1.1 × 103 A·m−1) for 10 s, a block scaffold (Φ 10 mm × 2 mm) showed an increase of 75 °C in temperature at the surface center. Simulated body fluid (SBF) soaking experiments revealed that the highly porous MBGC scaffold had good bioactivity. After immersion in SBF for 14 days, a hydroxyapatite layer covered the scaffold surface. Furthermore, cell experiments showed that the material was not cytotoxic to osteoblasts. An MGBC scaffold (Φ 10 × 2 mm) killed 56.8% of the MG-63 cells in a 30-mm Petri dish when exposed to AMF for 10 min. The good self-heating ability and bioactivity suggest that this novel magnetic glass–ceramic scaffold is a promising biomaterial, which may be used in the repair of bone defects after tumor resection. [ABSTRACT FROM AUTHOR]