The 60-year-old man was found in his bedroom by a domestic servant with a revolver by his side, said police officer Iftikhar Chatha, AP reported.
A doctor at Islamabad's Federal Government Services Hospital said the man died of a gunshot wound to the head. But the doctor, who spoke on condition of anonymity because he wasn't authorized to brief the media, said there would be no ruling on whether the death was suicide until an autopsy had been performed.
There was no immediate reaction from the Spanish embassy. Catha said the embassy had been informed and embassy officers had visited the scene.