The Poxburster in Darktide will charge at a player in your party, but unlike the Mutant they will blow themselves up on impact, doing high AOE damage. You should try to take them out from range before they can do this, but if that's not possible then it's best for the group to spread out in order to minimize the damage.
You can also bash the Pox Burster just before it hits you, and it will be knocked backwards before it explodes, doing no damage to you. Here is a quick video showcasing how to bash the Poxburster correctly:
Poxburster in Darktide
Puxburster charging at you