I think Lew is right when he says Ethiopian or Somalian. In the book 'African Arms and Armour' by Christopher Spring p 103. A couple of similar spears are depicted.
Besides the drawing is the following text :
"Somali and Danakil spear heads. Such blades often have a double concavity on either side of a raised median ridge though in less sophisticated exemples an impression of this structure is created on a flat surface simply by polishing a stripe of bright metal between two blackened segments."
Perhaps your spear head was a bit overpolished by its former owner.
