The unexpected surpluses are double previous estimates announced in the May budget.
Mr Frydenberg, who became Treasurer in August, announced the underlying cash balance for 2019/20 is now expected to reach a surplus of $4.1 billion, revised upwards from $2.2bn.
The Government has received $8.3 billion more than it expected in the first half of this financial year, thanks largely to greater collections of individual and company taxes.
The forecasted deficit for this year has been cut from $14.5 billion to $5.2 billion.
