The injured were taken to the government hospital in Fatehabad.
The bus was travelling from Jakhal Mandi in the district to Fatehabad town; the blast occurred at a place called Bhuna, the police said.
This is the third blast in Haryana in the last one month.
Earlier, a blast took place in an empty railway coach in Panipat district.
Last week, a low intensity blast in a moving Haryana Roadways bus left eight people injured.