The B6139 is a short link road to the south of Mansfield. With the exception of the western end, which was part of the B6021, the road was originally unclassified. It came into existence following the construction of the A38 Sutton in Ashfield bypass in the late 1980s.
Starting at the junction with the A38, the B6139 heads southeast through a mainly industrial landscape, crossing the Robin Hood railway line by means of a level crossing. There is a solitary house amongst the warehouses, this being the old gatekeeper's house for the crossing. After the crossing, there is a mini-roundabout, followed by a signalised crossroads, with the unclassified (and now a dead end) Cauldwell Road on the left, and the B6022 on the right.
The road then climbs steeply onto a ridge that affords views over the towns of Mansfield and Sutton. The road follows this ridge, which is one of the highest points in Nottinghamshire at 180 m altitude, passing the Sherwood Observatory and Coxmoor Golf Course on the left. The road then drops back down to meet up with the A611 at another set of lights.
The B6139 carries on in a near straight line to Thieves Wood, so named as allegedly Robin Hood and his merry men drove a particularly nasty band of robbers who were harassing the people of the Ravenshead area. Beyond the wood, the road turns to the right, to meet the B6020 at a T-junction. From here, it is a short distance to the left to Ravenshead.