Adult fleas can freeze to death or at least become less active during a cold snap or cold winter. Fleas are most active during the summertime and prefer temperatures in the 70s and 80s Fahrenheit.
There is one stage of the flea life cycle that is not as susceptible to cold temperatures, and that is the pupa stage in which the flea is encased in a cocoon like structure which protects it.
During this time, the flea can remain dormant when temperatures are extremely cold or freezing, and can emerge months later when the temperature warms up and becomes more favorable for its existence.
Flea eggs and pupa can remain on clothes and in the carpet and survive freezing temperatures without dying, and become active again when temperatures warm up.