There is not a class in Objective-C with a method for generating random numbers but C may be used. E.g: rand(), srand(), random(), srandom() and arc4random().
arc4random() tends to be preferred as it does not require seeding (it automatically initializes itself).
Examples:
int RandomNumber = arc4random() % 3; //Get random number from 0 - 2 (yes 2, not 3)
int RandomNumber = ((arc4random() % 901) + 100); // Get random number between 100 and 1000