Discoveries over the past two decades have revealed the remarkable ability of quantum materials to emulate relativistic properties of the vacuum, from Dirac cones in graphene to Dirac surface states of topological insulators. Yet one of the most elusive consequences of topology in quantum matter – the axionic bf E·bf B contribution to the electromagnetic response, predicted to produce strong magnetoelectric effects – remains experimentally challenging to detect. Here we report evidence for an axion-like magnetoelectric response obtained through scanning tunneling microscopy (STM) using a SmB₆ nanowire tip on an antiferromagnetic Fe₁₊ₓTe sample. Our measurements reveal a striking voltage-induced magnetization: millivolt biases generate measurable tip magnetizations that reverse with the voltage. The magnitude, tunability, and reversibility of this signal are consistent with an axion-like bf E · bf B coupling, which naturally accounts for the voltage-odd magnetic component of the tip spectral function while strongly constraining a conventional static-magnetism interpretation. Moreover, millivolt-scale control of spin polarization in a tunnel junction provides a new route for probing axionic electrodynamics and opens avenues for future STM and spintronic applications.