It's very common. so much so that if one's instruments don't mist up it's a cause for comment.
The causes and possible solutions have been discussed for generations, but no-one so far has come up with a definitive explanation (beyond the obvious, which is that there's warm moisture laden air inside the instruments which is being cooled to its dew point by the cold air in the upper part of the cockpit).
DaveW is currently drilling holes in his instruments in a strategy to promote better air flow. I've put in LED bulbs in an attempt to reduce the temperature inside the instruments. Others are toying with alternative solutions like wiring in additional fans.
1986 4/4 VVTi Sport, 2002 LR Defender, 1957 R4 CV, 2005 Ferrari Vipar