Our NF had flakey skin in his mane, do check for lice, as that can often cause it. We just gave him a wash with a medicated shampoo, (Head and Shoulders type) and it's not come back. Was quite difficult to wash as he has a mega thick mane.
a good shampoo and an extremely good rinse on a nice day! some oil or skin supplement for a month or so! its commonly a coming out of winter thing! check for extra friends!!!! and make sure you comb out regularly!
It's not uncommon at this time of year. Do make sure there arn't any parasites or skin conditions, and if there arn't good old head and shoulders usually does the trick!