Founder Stewart Rhodes and one other member, Kelly Meggs, were both found guilty on the rare charge.
The leader of a far-right militia has been found guilty of plotting to stop US President Joe Biden from taking office after the 2020 election.
A jury found Oath Keepers founder Stewart Rhodes guilty of the rare charge of seditious conspiracy following a two-month trial.
He plotted an armed rebellion to stop the transfer of power from Donald Trump to Mr Biden, prosecutors said.
Four more were on trial with him related to the Capitol riot on 6 January 2021.
Three of the group – Jessica Watkins, Kelly Meggs and Kenneth Harrelson – went inside the building during the attack.
Meggs was also found guilty of seditious conspiracy on Tuesday.
Three of the group members – Harrelson, Watkins and Caldwell – were found not guilty of seditious conspiracy.
All five of the group members were found guilty of obstruction of an official proceeding.
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