@prasvpatel this may be difficult to answer specifically because it all depends on your company's policy. From my experience, there are some companies that do not allow both mileage and fuel reimbursement. The reason is the mileage reimbursement amount is partially to cover cost of fuel.
However, there may be some companies who allow both. I think you will get a better answer by asking your SAP Concur site administrator or whomever is in charge of your company's spend policies.
Here in this Community, you will have so many different companies represented that all have varying policies. There should be someone at your company who can answer this question based on your company policy.