Some media persons, who had assembled at his residence to meet Hindustani Awam Morcha leaders, noticed a liquor bottle under a plant in the open.
Manjhi, who continues to live at 1, Anne Marg - the official residence of Bihar Chief Minister even after his replacement, said it was a huge security failure.
"If a person could enter the campus with a liquor bottle then bombs could also be brought in. I am facing a threat to my life and I have said this earlier also," he said.
"The place where the bottle was found is frequented by us. At times we also sit there. It is a mystery that the bottle suddenly appeared there," he added.
Manjhi on several occasions has asked people, especially those belonging to Scheduled Castes, to refrain from consuming liquor.
Asked about the breach in Manjhi's security, Bihar Police Additional Director General (Headquarters) Sunil Kumar said, "He has been provided with the required security provisioned to him. We are enquiring about this particular incident with the SSG Commandant responsible for his security.