A jury found Sammie Eaglebear Chavez, 19, not guilty of a similar, alternative charge, the Tulsa World reported.
The jury, which delivered its verdict Tuesday, recommended Chavez spend 30 months in prison and pay a $5,000 fine.
Chavez has been in jail since his arrest in December.
Testimony in the trial included witnesses at Bartlesville high school who heard him talk about his plan.
Police officers also testified about Chavez's journals, which discussed killings, and his computer hard drive, which indicated he had researched bombs and mass shootings at Columbine High School and Virginia Tech University.
Chavez argued he was only joking about the mass shooting and that he wasn't serious about injuring anyone at the school, the World reported.