One of the suspects, James Ujaama, 36, was arrested last week in Denver.
Sources told Fox News that agents found documents about water poisoning - as well as other terrorism-related evidence - in his Denver apartment.
The other suspect, Semi Osman, also had instructions about poisoning water on him when he was arrested, the report said.
The government believes that Ujaama - whose brother, Mustafa, is the founder of a now-closed mosque in Seattle that is under scrutiny for links to al Qaeda - acted as a courier, delivering laptop computers to the Taliban.
Fox News also reported that investigators believe that members of the mosque were trying to establish a terrorist-training camp in Oregon and that Mustafa Ujaama visited the state, scouting a suitable location.
Sources told the network that the Ujaama brothers and Osman are tied to a radical, London-based cleric named Sheik Abu Hamza al-Masri, a one-eyed mullah who is wanted in Yemen on terrorism charges.
Source: Fox News