Point defects have been successfully utilized in various quantum technologies, serving as quantum qubits for quantum computation, single-photon emitters for quantum communication, and nanoscale sensors for quantum metrology. However, their further development faces key challenges, particularly in discovering and exploring suitable defect-host systems that meet the necessary criteria for quantum applications. Here, using polarization-resolved Raman spectroscopy and terahertz absorption spectroscopy, we discover three distinct chromium-vacancy-induced excitations in the uniaxial antiferromagnetic insulator, Cr₂O₃. These vacancy-induced excitations have an energy scale of a few tens of millielectronvolts and are twofold degenerate, and the lowest one at 64 cm⁻¹ is sharp and sensitive to the external magnetic field along the easy-axis direction, particularly close to the spin-flop regime around 6T, where the mode softens from 64 to 27cm⁻¹. Based on the defect supercell first-principles calculations, we interpret the mode at 64 cm⁻¹ as a local magnetic excitation of the local moment within the chromium vacancy state. Our results establish that the magnetic defect states in Cr₂O₃ have potential for quantum applications.