For appearing in Civil Service Exam you should be a graduate or equivalent in any discipline from a recognised university. However you can also apply if you have appeared in the final year but do not have the result.
In case you have passed the final year of MBBS or any Medical degree Examination but are yet to complete the internship can also appear for the Main Examination. However you must submit along with your Main Examination application, a certificate from the concerned authority of the University / Institution that they have passed the final professional medical examination.
Besides you must be a citizen of India as per government guidelines and between the age group of 21 years -30 years on 1st August in which the examination is being held.