Officers in Dayton say William Schooler, 70, was gunned down at around 12.30pm in his office at St Peter's Missionary Baptist Church on Sunday.
American media reported the shooting happened during a service with around 20 others in the church.
Daniel Schooler
His brother Daniel Schooler, 68, was arrested and is expected to be charged with murder on Monday.
Detectives believe the pastor was the intended victim of the shooting.
Revd Schooler was a former interim president of the Dayton school board and current president of the local Baptist ministers union.
