Lieutenant Costa was a Starfleet engineer stationed on board the USS Enterprise-D in 2366.
While the ship was on the way to Nahmi IV, he was ordered to realign the magnetic capacitors together with his colleague Duffy. (TNG: "Hollow Pursuits")
Costa was one of only four crewmembers of the Enterprise-D (the others being Data, Geordi La Forge and Miles O'Brien) who had the skill to reprogram thirty to forty isolinear chips in half a dozen subsystems in a short amount of time. (TNG: "The Mind's Eye")
Costa was played by an unknown actor and only mentioned in "The Mind's Eye".