True for all the Galilean Moons more or less. Their orbits all lie within the Jovian equivalent of the Van Allen belts. And Jupiter's magnetic field is much stronger than earth's.
Jupiter and Io have a very interesting symbiosis. Jupiter melts Io to form dusty volcanos. It then magnetically sweeps Io clean of dust. The dust forms a plasma ring that enhances the same magnetic field.
Io, meanwhile, is 35 Sv/day. Location really matters among the four Galilean moons.