The incident took place at Usmanpur colony last evening when Shrashav (12) and his friend Puti (15) riding a bicycle were hit by a bus from the front, they said.
While Shrasha, who came under the bus died on the spot, Puti was thrown away and sustained serious injuries, police said.
Irate mob then thrashed its driver Suresh and damaged the bus by pelting stones. The driver was also seriously injured due to the beating, they said.
Police later reached the spot and held the driver. While the victim's body has been sent for postmortem, Puti has been taken to a hospital.