1. Extremely modest or shy
   "cheerfully bearing reproaches but shamefaced at praise"
    
2. Showing a sense of shame
   "The shamefaced student apologized for cheating on the test";
   - sheepish
    
3. Showing a sense of guilt
   "the hangdog and shamefaced air of the retreating enemy";
   - guilty, hangdog, shamed

See also: ashamed, modest