The sweep of the building leased to call center company Maximus is being done as a precaution, Boise police spokeswoman Lynn Hightower emphasized.
By noon, police were cleared from the scene, and no dangerous devices were found, she said.
Employees were evacuated from Maximus' building, and those leaving the campus were not allowed to return. An Ada County sheriff's deputy at the scene told the Statesman that they were investigating a threat. A Statesman reporter was later asked to leave the HP campus.
In an email, Hightower said preliminary information was that a note prompted the safety sweep. Police are working with private security.
"At this time, there is no reason to believe there is a widespread public safety threat on the campus," Hightower wrote. "Some employees have been asked to leave the building while the search takes place. Officers on scene say the situation is going smoothly, people are cooperating."
Building security declined to comment. HP employees were not evacuated. In an email obtained by the Statesman, HP's Crisis Management team said all employees currently at HP should stay inside, and all others should stay away from the campus.
Maximus spokeswoman Lisa Miles released this statement on behalf of the company.
"Today we received an anonymous threat at our Boise facility," she wrote. "Our first priority is the safety of our employees, and in response, we evacuated all personnel from the building and immediately alerted law enforcement. All employees are accounted for and safe. The authorities conducted a sweep of the facility and we expect operations to resume in the morning. MAXIMUS has been working with law enforcement and we have implemented additional security measures at the facility."
Maximus runs call centers to serve health insurance exchanges around the country as part of the Affordable Care Act.
This is the second time this fall that police have been called out to the Maximus building. A similar incident occurred Sept. 26. Police determined then that there was no threat to public safety.