It depends on the size of the tank and what else you had in mind. If it is a 5 gallon of smaller, no you shouldn't get any other fish. If it is 10 gallons or larger then you can get a few others but a lot of tropical species don't get along well with Bettas. Either the betta will get jealous of the other fish's fins and attack it or the other fish will try to eat the betta's fins.
It will also depend on your Betta's attitude, if he's agressive then he shouldn't have many friends but if he's passive he might get along okay.