Sheriff Russ Isham of Marion County declined to release the suspect's name, saying it would jeopardize the integrity of the investigation and the safety of officers still working the case.
"We do believe the person responsible for the bombing is in custody," Deputy District Attorney Courtland Geyer said late Sunday.
The suspect was arrested in Salem, located just south of Woodburn, the small city south of Portland where Friday's bombing occurred.
Officers made the arrest shortly after Sheriff Russ Isham of Marion County released surveillance photos of a "person of interest." Geyer would not say if a tip led to the arrest.
He also wouldn't disclose if the man in the photos, apparently taken with a security camera, is the same person in custody.
Isham would not release the precise location where the arrest took place, and said the suspect's name likely wouldn't be released until Monday afternoon.
"I'm really proud of those who tirelessly worked to get us to this point and am humbled by the community's support," Isham said. "We know there is still a lot of hard work ahead of us, but this development will help bring relief to the local community and the officer's families."