The defendant, identified only by his initials AS, was "sentenced to death by hanging after being convicted of collaborating with the occupation," the source said.
There were no further details on the allegations against him.
Under Palestinian law, those convicted of collaborating, murder or drug trafficking face the death penalty.
All execution orders must in theory be approved by Palestinian president Mahmud Abbas before they can be carried out, but Hamas, the Islamist movement that rules the Gaza Strip, no longer recognises his legitimacy.
In Gaza, beyond death sentences handed out by courts, Hamas has also carried out summary executions for collaborating with Israel, sometimes in public places.
The most prominent occurred during last summer's 50-day war between Palestinian militants in the territory and Israel, when a firing squad of men in uniforms from Hamas' armed wing shot dead six people in front of Gaza City's main mosque.