Mehran Hussain, 24, and Umair Hussain, 25, both of Chingford, east London, had been accused of failing to disclose information about their brother Nabeel, a suspect in the alleged conspiracy.
Nabeel Hussain is one of 11 men charged with conspiracy to murder and preparing an act of terrorism in relation to the alleged plot, which was foiled in a massive British police swoop on August 10.
The defendants are British, most of them of Pakistani origin, and aged between 17 and 35.
District Judge Quentin Purdy discharged the pair following a committal hearing at the City of Westminster Magistrates' Court in central London.
Purdy told them there was "insufficient material" to send them to trial but, if further evidence came to light, prosecutors could still take action.
A statement from the Crown Prosecution Service, which is responsible for prosecutions in England and Wales, said it respected the court's decision.
Revelations about the alleged plot to blow up transatlantic airliners sparked a massive security clampdown, which led to widespread disruption at British airports at the height of the summer holiday rush.
Umair Hussain was among 19 named people whose assets were frozen by Britain's finance ministry, the Treasury, and central bank, the Bank of England, on August 11.
A finance ministry spokesman told AFP they did not comment on individual cases but sources said the list had not been amended on Wednesday.
Keeping people on the financial sanctions list requires a lower burden than the criminal courts -- "reasonable suspicion" rather than "beyond all reasonable doubt".

Copyright AFP (Agence France-Presse), 2006