I have 4 Green Tiger Barbs, and one of them is being agressive towards the three others. Like chasing and looks like biteing at the other barbs.
Is there anything i can do to stop the agressive Tiger Barb?
Or is it just natural and i should let it go?

It's natural for them, but you do need a bigger school of them it will give more to pick on and set the natural heirarchy. How big is the tank?

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The more you get, the less aggression you will see. I have 6 along with a few other types of barbs and a shark. They are all happy. Feeding to little will also cause them to act more aggressive.

Tiger barbs should not be kept in one tank with slowly moving fish with dragging fins or any other body parts. They will be nipping on them. Also, feed your tiger barbs well, better with live food. I treat them with raw meat products, such as liver, chicken or turkey and any kind of raw fish. Choose soft, lean parts without tendons, skin or other connecting tissue. I take a piece of wood and cut meat with razor into small convenient to feed pieces. Better rinse it in water prior to feeding in the tank to avoid excessive pollution. A well fed tiger barb is playful and less prone to nipping on body of other fish. I also feed them with grindal worms and freshwater crustacea and small insect larvae, when I can collect them in the wild. Tiger barbs eat some vegetable food, but they are not vegetarians. They like meat.

I have found what that it's best to keep them in groups of 5 or. Always in odd numbers. I have a pack of 9 ranging from 1/2" to 3". Then chase each other from time. Just make sure they have a safe zone to hide. Like Ufimyh said, don't keep slow moving fish or long fin fish with them.