More info would help here A.... what are you feeding him? Is it the same food day after day? At 6 months he can hold things - are you giving him food he can pick up and play with or feeding him with a spoon?
Meal times are exploration time for babies. They need to feel their food in their hands and taste different flavors and textures in order to stay interested.
If you aren't doing it already, abandon the spoon feeding as his primary source of solid food. Cut up brightly colored vegetables and fruit (carrots, potatoes, watermelon and bananas, etc...) and let him explore them on his tray.
When meal time is more interesting, you can get spoonfuls in while he explores with his eyes and hands the fun stuff in front of him.
And of course, yes, he could be teething.