Keister spoke to Leone Stars goal keeper coach Tamba Moses and logistics officer Alusine Kabba three weeks ago, and allegedly called the SLFA President Isha Johansen 'corrupt.'
Moses and Kabba have also been banned indefinitely.
'These officials were found guilty of gross misconduct by bringing the name of the institution into disrepute," the SLFA said in a statement.
"The SLFA management will subsequently inform the suspended officials with regards development on their employment status."
The SLFA secretary general Christopher Kamara also wrote to Keister about his previous conduct:
"You have had countless verbal and written warnings about your conduct."
Before his ban was announced, Keister - a former Sierra Leone international - had already issued a statement apologising for what he had said in the leaked audio.
Keister, who was appointed eleven weeks ago, has only taken charge of Sierra Leone for one official match, a 1-0 win over Kenya in a 2019 Africa Cup of Nations Cup qualifier in Freetown in June.
The Leone Stars' next competitive game is away to Ethiopia in March next year.
John Keister, the head coach of Sierra Leone's national team, has been suspended indefinitely by the Sierra Leone Football Association (SLFA) following the leak of an audio conversation where he is accused of bringing the SLFA 'into disrepute.'