Can a human being reside both in this world and Nirvana at the same time?

I've heard Samsara as the term to describe a world with suffering. And it's my simple understanding that Nirvana is the absence of suffering. Correct me if I'm mistaken. My question is fairly simple, i.e., do all beings in this world "get reborn" through karma, or are there ascended beings in this world, living as human beings, free of all suffering?