Hello I Recently Got A Cat And Noticed That She

Hello I recently got a cat and noticed that she had scabs towards the end of her back by the tail area is this caused by fleas ? she has been treated prior to getting her and the last owners did say she had fleas ..Just wondering will the scabs fall off on there own I found them when I went to brush her fur and got towards the back area she yelled so it must still be sore to her Thanks for your time...Jeremie