The Alpha Onias system was an uninhabited but strategically significant planetary system in the Beta Quadrant. This system, located within the Onias sector, was located near the Romulan Neutral Zone in the mid-24th century.
In 2367, subspace anomalies were detected in this system, originating from Alpha Onias III. As there had been rumors about a secret Romulan base in the region for quite some time, the USS Enterprise-D proceeded to investigate it further. (TNG: "Future Imperfect"; DIS: "Magic to Make the Sanest Man Go Mad")