This happens to my car cause I don't use AC and always keep my vents open for fresh air.
Usually I use a desiccant like Dri-Z-Air (WalMart, CT, Lordco) but recently discovered a smaller container at Dollarama called DampTrap for $1.25. I just put it on my dash after I shut the car off.
Garden Gnome at Home: A Simple Moisture Solution
DRI-Z-AIRŪ DEHUMIDIFIER - MOISTURE ABSORBER - MADE IN THE USA
edit: also a must if you store your car outdoors.