Are my striped tetra's mating?

Interesting juxtaposition of ideas in the first answer. A schooling fish driving fish of its species out of the territory. That could only be true if the tank was extremely small. I am guessing that your " striped tetras" are really known on the market as Black Tetras, the correct name being Gymnocorymbus ternetzi. They are also called Black skirt Tetras. The behavior you are seeing is typical for these "nippy" fish. The best solution would be to add several more of the same kind of fish, thus spreading the nipping around to more fish. If your fish are indeed Black Tetras (the stripes are actually vertical) and thus described more correctly as "bars" ing young individuals can be difficult.