Hazare, 81, last week broke his week-long fast over his demand for appointment of anti-corruption watchdogs.
"Anna is suffering from weakness and other health issues due to lack of blood supply to his brain," Dr Bapu Kandekar, who examined the activist, said.
"Hazare, who lives in Ralegan Siddhi village in Ahmednagar district, complained of some health problems and was brought here in the morning," his aide said.
He underwent an MRI (magnetic resonance imaging) scan at a diagnostics centre here.
"He was later admitted to a private hospital as suggested by doctors," Hazare's aide Shyam Asawa told media.
"Hazare has been suffering from neurological problems for the last two days," Asawa said.