Yes, fleas will eat human blood if humans are present and available as hosts, but humans are not a flea’s first choice for food.
There are many different species of flea, each one having evolved to specialize for a specific host, such as a dog or cat. None of these flea species have specialized in feeding on human blood.
But if a person lives in a home that is infested with the fleas of one of his pets, there is a risk that he will also be bitten as well.
Fleas require a blood meal from a warm-blooded vertebrate in order to reach the adult stage of their life cycle and reproduce. If they cannot obtain blood from the primary host, they will certainly eat human blood in its stead.