While I am no expert, I have come across many articles and catalogues which claim that items like this are strap ends (that is the went on the end of a leather belt or horness strap). They are often described as Avar or Slav and dated to 6th-9th centuries. I suspect that the exact shape and decoration (they often seem to have line designs on one face
and yours appears to as well) would determine it more closely if you could find the right reference guide. This would fit if yours is a Balkan find.