Hi there, according to this article on baby's milestones (link below), it is actually very normal :) At that age, baby will learn how to prop herself up on her arms and hold her chest off the ground, like a mini-pushup.
Not too long after, she will be able to sit momentarily without assistance. Don't worry about baby being in the position for too long. When she's tired, she'll know when to stop and you should stand by to provide support and surround baby with pillows to cushion a possible fall.
http://www.babycenter.com/0_baby-milestones-sitting_6505.bc