It is likely that your 2D shape is importing as a spline and not a solid. A spline has no virtual mass, only coordinates.
You could construct a polygon on top of the spline.
You could extrude the spline with NURBS to create mass.
Or there might be some other function in your 3D app to generate a solid from a spline.
Note: Enabling Rulers in Illustrator allows you to define the splines center - Click and drag the ruler corner (on the top-left side of the artboard) to the desired center of the spline (path).