County Manager David Smith and Assistant County Manager Sandi Wilson told The Arizona Republic Thursday they are scheduled to testify Jan. 13 before the grand jury.
Arpaio said he doesn't know anything about the investigation.
"I have no idea what's going on in the grand jury," he said. "I am not going to comment about grand jury activity -- no matter what you hear."
The Republic said there has been talk for months that sheriff's department officials have been called before a federal grand jury. Sources have confirmed a captain and two chief deputies have testified, the newspaper said.
The content of the officials' testimony is not known.
Sheriff's department investigations into county officials during the past year have resulted in the indictment of two members of the Maricopa County Board of Supervisors and a complaint in federal court of a conspiracy against supervisors, judges and other officials, including Smith and Wilson, the Republic reported.
The newspaper reported in May FBI agents had been contacting county officials, asking whether Arpaio had abused his authority.
A Justice Department spokesman told the newspaper the department would have no comment on the report.