If it doesn't have big open knotholes in the face, you can laminate over it. If it's got open knotholes, splits, or other surface defects, I'd fill them with something (bondo, wood putty) before laminating over it.
On the other hand, you can buy a cheap belt sander for about the same cost as a sheet of laminate. With a couple of belts you could get a stainable or paintable surface in short order.
On yet another hand, you could buy a sanded sheet of B/C plywood cheaper than either of the other two options. Stain and finish the good side of that one, and glue your existing sheet underneath it. You get a thick desktop that won't warp and looks like furniture when finished.