Parts of Wrexham, Powys and south east Wales are the areas most likely to be affected.
A yellow "be aware" warning is in place from 16:00 GMT on Sunday until 10:00 on Monday.
Forecasters said the "main uncertainty" surrounded whether the fog persists into the Monday morning rush hour.
Motorists could face potentially hazardous driving conditions and subsequent delays caused by fog, the Met Office has warned.