No, guppies are not aggressive. Guppies are generally peaceful and friendly fish if kept in proper conditions. Guppies get along well with other guppies as well as other fish species.
With that said, guppies can still show aggression if the tank is overcrowded or there’s food scarcity. Moreover, male guppies tend to be more aggressive than females. Male guppies may chase female guppies around while trying to mate, and may even chase other males to assert dominance.
To prevent aggression, make sure their tank is not overcrowded and feed them properly. Additionally, ensure the male guppies don’t outnumber the females by using the 1:2 ratio, males to females.