Not a jersey as such, but I’m using these at the moment. They are to all intents and purposes a Bamboo and cotton T-shirt, but broken riders/trail42/exempt clothing sell them for mountain biking, albeit roughly twice the price because of the logos they print onto them.
They behave pretty much like a normal cycle jersey, nice and cool, however:
1: If you wear a backpack, it can become a bit sweaty underneath it, and being a thicker material, it doesn’t dissipate that moisture as fast as a standard jersey
2: Being bamboo, these tops shrink in the wash, although only one of my tops has shown any shrinkage so far.
3: You can wear them off the bike as they are a T-shirt.