The boy was arrested on Tuesday at an address in west London on suspicion of dissemination of terrorist material. He has since been released on police bail until a date in mid-June.
"While it is still very rare for such a young person to be arrested for a terrorism offence, in recent times we have seen a worrying increase in the number of teenagers being drawn into terrorism," said Richard Smith, head of London police's Counter Terrorism Command.
"This particular investigation remains ongoing, but more broadly, we work closely with a whole range of partners to try and protect and divert young, vulnerable people away from extremism and terrorism."
In February last year, a boy who headed a neo-Nazi group and carried out his first offence aged just 13, was convicted of terrorism offences. Last July another 13-year-old was arrested and later admitted possessing information useful to a terrorist.
Police have previously warned than young people, mainly boys in their early teens, were becoming self-radicalised online and then progressing to actually planning terrorist attacks.
(Reporting by Michael Holden; editing by William James)
