Back Brook is a tributary of Pike Run in Somerset County, New Jersey in the United States. It is located on the east side of Sourland Mountain.
Back Brook starts at , on the edge of Sourland Mountain. It flows eastward, crossing Blawenburg-Belle Mead Road and Sunset Road before running through Schuss Woods and the McAlpin Farm Easement. It then crosses Route 206 and flows through Oxbridge before entering Pike Run at .