Preheat oven to 325 degrees F (165 degrees C). Grease the bottom of a 9x13 inch pan.
In a large bowl, combine flour and brown sugar. Cut in peanut butter and margarine until crumbly. Reserve 1 cup of crumb mixture. To the remaining crumb mixture, pour in milk, eggs, vanilla, baking powder and baking soda. mix well and pour into pan. Sprinkle top with reserved crumb mixture and chocolate chips.
Bake in the preheated oven for 45 to 50 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.