I found that work is Force * Displacement When a force is applied on a body and the body is displaced My query is why mass of the body is not considered when work is calculated? Please answer.
To calculate the work done by a force, the mass of the object is irrelevant. If you push with the same force for the same displacement, the work you do is the same regardless of the object's mass. And if that's the only force acting, then the change in the object's kinetic energy will be the same, regardless of its mass. (The resulting speed will depend on the mass, though.)
Where possible, it is best to keep a definition simple - involving as few variables as possible. There are a million different ways of doing 1kJ of work, some involving a lot of change in Kinetic Energy (throwing something) and some involving more of a change in Potential Energy (raising something slowly). By defining work in terms of force times displacement in the direction of the force (- important to include that!) you eliminate the need to consider what the work is actually 'doing', because that is not necessarily relevant to the energy that is put into the process.