At 1545 GMT, the rand was 0.86% firmer at 14.5720 per dollar compared to a close of 14.6950 overnight in New York.
Mboweni is likely to raise the budget deficit because of costs related to the state-owned power utility Eskom, a Reuters poll showed.
Treasury’s best option will be to rely heavily on expenditure cuts and the lifting of economic growth through structural policy adjustments, said Old Mutual' s chief economist Johann Els.
"If the Eskom plan and MTBPS (budget) are received as acceptable and Moody’s keeps our rating outlook unchanged at stable, rand and bond relief rallies are likely," Els said.
In fixed income, the yield on the benchmark government bond due in 2026 was down 4.5 basis points to 8.17%.
Stocks were down, with the Johannesburg Stock Exchange's Top-40 Index slipping 0.54% to 48,858 points, and the broader all share index closing 0.61% lower at 55,141 points.
Gold miners were the biggest winners of the blue-chip index for the second day in a row, with Goldfields up 1.3%, followed by Sibanye-Stillwater and AngloGold Ashanti, both up more than 1%.
The miners were benefiting from a rise in the gold price, which was set for its best week in five weeks on Friday as uncertainty around Brexit, weak U.S. economic data and worries about trade pushed investors towards safe havens.
The biggest loser of the day was the world's largest brewer Anheuser-Busch InBev, whose Johannesburg-listed stock lost almost 10% after a profit warning that wiped $13 billion of the company's market value.
(Reporting by Mfuneko Toyana and Emma Rumney; Editing by Toby Chopra)