The body was found Friday near the Rolling Acres shopping mall in Akron, agency spokeswoman Vicki Anderson told The Associated Press.
The cause of death and identity are under investigation. The FBI is working on the supposition that the body may be that of Timothy Kern, 47, of Massillon, who hasn't been seen in more than a week, Anderson said.
"Do we think it might be? Maybe," Anderson said. "He's missing. We haven't been able to find him. It could possibly be, but we just don't know that yet."
Anderson declined to specify how authorities discovered the body, saying only it was through "information."
Kern answered the same ad for a farm hand that authorities say led to the shooting death of Norfolk, Va., resident David Pauley, 51, in a rural area 90 miles south of Akron. A South Carolina man reported answering the ad but managing to escape after being shot Nov. 6.
Two people from the Akron area are in custody: a high school student who has been charged with attempted murder and 52-year-old Richard Beasley, who is in jail on unrelated charges.
Another man who responded to the ad has said he met Beasley at a food court at a different mall in the Akron area on Oct. 10. Ron Sanson, of Stow, was told the man was looking for an older, single or divorced person to watch over a 688-acre farm in southeast Ohio - the kind of man, Sanson said, whose disappearance might not be quickly noticed.
Sanson and Kern are both divorced. So was Pauley.
Sanson, 58, said he filled out an application and talked for about 20 minutes with Beasley about a $300-a-week job overseeing a swath of land a mile from the nearest neighbor and living rent-free in a two-bedroom trailer with opportunities to hunt and fish, as well as free access to ATVs and snowmobiles.
Law enforcement officials have released few details because of a judge's gag order. The sheriff in Noble County, where Pauley and the South Carolina man were shot, previously said it was unclear how long the ad was online or whether there were other victims.
Associated Press writers JoAnne Viviano and Andrew Welsh-Huggins in Columbus contributed to this report.