It is the first known case of a British military worker contracting the disease. Britain has an extensive anti-Ebola effort underway in Sierra Leone.
A public health spokesman said no details about the health care worker's condition would be released.
Two British nurses who contracted the disease while treating patients in Sierra Leone last year survived after being brought back to Britain for specialist treatment.
Contingency plans have called for infected British health care workers to be transferred to London for treatment in a special unit at the Royal Free Hospital.