The auctioneers said Lennon played the guitar, which is expected to exceed its estimate of $600,000 to $800,000, on the Beatles' 1965 album "Help!"
The festival was held during dinner time on Saturday and Sunday, the hotel said in a statement on Sunday.
The buffet was priced at Tk 2495 plus taxes and service charge per person with a buy-one-get-one-free offer.
Vietnamese Ambassador Tran Van Khoa organised a private party in the hotel on Friday to announce the event.
Some VIPs, including the ambassadors of several countries, were present at the party, according to the statement.