Randy Graham also was found guilty Tuesday of growing marijuana to finance the conspiracy. The federal jury acquitted Graham on charges of possessing illegal machine guns seized from another militia member's home.
Graham, 42, faces up to 30 years in prison when he is sentenced May 5.
Assistant U.S. Attorney Lloyd Meyer called the verdict ``tremendous'' even though jurors rejected three counts of the nine-count indictment.
``An armed and dangerous man is no longer walking the streets,'' he said.
Defense lawyer Jeffrey O'Hara said no decision about an appeal would be made until after sentencing. He had argued that Graham was being prosecuted for expressing unpopular beliefs in private telephone conversations the FBI recorded under court order.
Prosecutors said the case had little to do with simple talk.
``He's being prosecuted for plotting to do terrible things he didn't do because he was stopped,'' Meyer said during closing arguments, standing in front of photos and maps the government contended targets Graham planned to attack. ``How much further did they have to go before someone got hurt?''
Graham is the second member of the militia group to be convicted in the case. In November, a federal jury found Bradford Metcalf, 47, guilty on weapons and conspiracy charges. He will be sentenced in April.
The charges stem from a raid last year at Metcalf's home where authorities seized thousands of rounds of ammunition and loaded weapons.
A third co-defendant, Kenneth Carter, 47, is cooperating with the government and will be sentenced in April.