Not always. PSIG is just a measure of pressure difference between two volumes of fluid. Generally, those volumes are some pressurized vessel and open atmosphere. If you took a vessel pressurized to 22.4 psig at sea level and put it under ~18 feet of water, it would now be 0 psig, even though what's inside hasn't changed. If you stuck a gage on the outside of the space station to measure the inside pressure, PSIG and PSIA would be identical, since the reference is 0 psi.
For many purposes though, PSIA = PSIG + 14.7 is adequate.