The policeman was shot dead by two armed men on motorcycles in the Rigasa area of the city, said Kaduna state police commissioner Ballah Nassarawa.
"We lost a policeman to two gunmen who shot him while he was returning from work and we think it was a robbery incident," Nassarawa said.
"From all indications the gunmen were after the policeman`s motorcycle," he said.
But residents doubted the police chief`s claim, saying the attackers did not steal the motorcycle.
"The gunmen rode abreast the policeman and shot him twice and sped off," Rigasa resident Rabiu Tukur said. "They did not make any attempt to take his motorcycle which raised the fear that the attackers could be members of Boko Haram."
The shooting came as security authorities grappled with a worsening Boko Haram threat in several northern areas.
South of Kaduna, in Nigeria`s second city of Kano, the group staged its deadliest ever offensive on January 20, targetting primarily police stations with coordinated bomb and gun attacks that killed at least 185 people. (*)