A number of empty wagons toppled on to tracks at 4:05pm at Carrbridge station in Inverness-shire, Network Rail said. It is not known if the freezing weather contributed to the derailment.
Northern Constabulary said there were two people on the freight train, one of whom was treated for minor injuries.
First ScotRail said a replacement bus service was running between Inverness and Aviemore.
A Network Rail spokeswoman said: "It was the 1:14pm freight service from Inverness to Mossend yard depot. It is a ten-wagon vehicle. We do not know the cause.
"The locomotive is upright. Some of the empty wagons it was carrying have gone over across the lines. We are focused on getting those back upright. The Inverness to Aviemore route is blocked until further notice.
"There will be some disruption but it is a remote part of the network."