The incident occurred at around 7.30pm when Head Constable, identified as S Raja Manickam (47), was found lying in a pool of blood after his colleagues heard gun shots fired inside the National Human Rights Commission (NHRC) headquarters.
"Manickam was immediately rushed to a nearby hospital but he was pronounced dead on arrival. The exact cause of his taking the extreme step is being ascertained. Prima facie, it looks to be a case of suicide," official sources said.
"He used a pistol present in the armoury to shoot himself," they said.
Officials said the Head Constable also took a roll-call of his unit personnel in the evening and he seemed to be all right then.
Senior CISF officials and Delhi Police reached the incident spot soon after and apart from a regular case the paramilitary will conduct an inquiry into the case, they said.
Manickam had joined the Central Industrial Security Force in 1991.