Climbing Mt. Fuji is Very dangerous outside of official climbing season.
(In general, Mt. Fuji is open to climbers from early July to September 10th.)
Please refrain from climbing outside of the period of official climbing season.

Climbing Mt. Fuji safely and comfortably in a crowded area
Three off-season regulations
Movie Guide [7 rules of safety for climbers of Mt.Fuji.] (English only)
Mt. Fuji World Heritage Centre, Shizuoka
Official Web Site for Mt. Fuji Climbing
Your Official Guide for Japan Travel