The Bahrain Youth Society for Human Rights says a boy died during an operation by security forces to break up a small pro-democracy protest.
It says Ali Jawad Ahmed, 14, was among a small crowd who had gathered overnight in the village of Sitra.
The group said security forces personnel used ''excessive force''.
One member told the BBC that Ahmed was hit in the face by the canister. The society has published a photograph showing the boy with blood seeping from his mouth.
BNA, the state news agency, says police have started an investigation.
More than 30 people have been killed in Bahrain since protests began in February