The National Testing Agency NTA is a government by formulated by MHRD i.e. Ministry of Human Resources Development of Government of India to administer the entrance examinations. For now both JEE Main and NEET are held by Central Board of Secondary education. However CBSE expressed displeasure in conducting entrance examination as it gets over burdened.
Also need was felt since long to establish a centralized testing agency. Now NTA is formulated and to begin with it will conduct national level engineering and medical admission tests for under graduate courses. The agency may hold JEE Main and NEET examinations twice in a year.
In my personal opinion this step will be good for candidates and in favor as they will get chance to write two tests in a year.