GERMANY—Prosecutors say they have charged a 60-year-old German who worked at NATO’s air command headquarters at Ramstein Air Base with stealing secret data.

Markus Koehler, a spokesman for federal prosecutors, said in a statement the suspect—identified only as Manfred K. in accordance with German privacy rules—was arrested Monday on charges of obtaining state secrets with the intent to provide them to an unidentified third party.

The civilian NATO employee is alleged to have obtained the data and then transferred it to his private computer.

Koehler would not say Tuesday when the data were allegedly stolen nor whether any of it was passed along, citing the ongoing investigation.

NATO’s press office at Ramstein did not immediately return calls and its headquarters in Brussels had no immediate comment.