The bikers shot twice at Kumar and immediately fled the scene.
Kumar who was in a critical condition was rushed to Bihar Sharif Sadar hospital, but it was found that he had died in the way to the centre.
As per the locals, Kumar had gone out for a walk following his daily routine and had reached Milkipur village when the incident took place.
A huge number of people gathered at the hospital to console family members as soon as the news of his death broke out.
The deceased professor belonged to a family involved in business, which has led to an outrage among the traders and business groups.
In a separate incident, a compounder was also shot dead in broad daylight in Darbhanga.
A police investigation is underway.