I find no mention of this man in:
1) Lee's Colonels by Robert K. Krick
2) Staff Officers in Gray by R.E.L. Krick
3) A Guide to Virginia Military Organizations by Lee Wallace
4) Compiled Service Records of the Confederate Soldiers Who Served in Organizations Raised Directly by the Confederate Government; (National Archives Microfilm Publication M258, 123 rolls); War Department Collection of Confederate Records, Record Group 109; National Archives, Washington, D.C.
Since Harper was born in 1807, he may have served in a pre-war militia unit.