Steven, 61, was arrested in his Puyallup, Wash., home and booked on suspicion of 14 counts of voyeurism and one count of possessing depictions of minors engaged in sexually explicit conduct, reports the Salt Lake City Tribune.
Bail was not immediately set and the arrest is unrelated to Susan's disappearance, states the newspaper, quoting authorities.
Tacoma's News Tribune reports that Pierce County detectives discovered more than 2,000 images of girls and women in Steven's home during a search last month for evidence related to his daughter-in-law's disappearance.
Some of the subjects in the images were videotaped without their knowledge and were as young as 8 and 10, said prosecutor Mark Lindquist, adding that the Class C felony charges Powell faces carry a standard sentence of up to five years in prison.
Powell is scheduled to be arraigned Friday.
Sons Taken AwaySusan Powell's husband (and Steven Powell's son), Josh Powell, is living at the Puyallup house along with his two boys by Susan. But, reports the Tribune, the youngsters were taken into protective custody by Washington state child welfare officials in the aftermath of their grandfather's arrest.
Recently, Steven Powell was interviewed on national TV programs, claiming that his daughter-in-law used to sexually proposition him. He also had plans to sell her personal journal, but was prevented from doing so after legal action taken by Susan's parents, Chuck and Judy Cox.
"He's creepy and I think this kind of proves that," Pierce County sheriff's spokesman Ed Troyer told Seattle TV station KIRO on Thursday. "Something is up there, obviously we're continuing to work the case and as we find these things, it's disturbing."
Josh Powell initially told investigators he last saw his wife the night of Sunday, Dec. 6, 2009, at their then-home in West Valley City, Utah, southwest of Salt Lake City, when he took their sons for an overnight camping trip. He has since refused to talk to authorities and has suggested his wife ran off with another man.