In the weekly bond auction held on Tuesday, bonds worth 23.6 trillion rials ($94 million) were sold to investors with zero contribution from banks.
The main buyers were security underwriters who bought bonds worth 20 trillion rials ($80 million), accounting for more than 85% of the total.
The remaining was bought by retail and institutional investors at the stock market, according to a press release posted on CBI's website.
Bonds on offer totaled 42.4 trillion rials ($166 million) with yields ranging from 20.5% to 21.5% for two- and three-year maturities.
CBI said it will offer 38.5 trillion rials ($154 million) in the next auction on Feb. 23.
Starting last May, the auctions are among government measures to help plug its deepening budget deficits. Banks and credit institutions emerged as the biggest buyers of government bonds in the initial rounds of auctions, but later stock market investors stepped in.
The central bank has so far held 38 auctions and generated close to 1,090 trillion rials ($4.3 billion). Banks and investment funds contributed 52% of the amount while 48% of the bonds were bought in the stock market.
Estimations by the Persian economic website Eghtesad News put the government's budget deficit at 160 trillion rials ($640 million), which must be procured through weekly auctions by the yearend on March 20.
Bonds have also reportedly helped restrain government borrowing from the CBI that fueled inflation by increasing the monetary base.
Earlier in the month, CBI Governor Abdolnasser Hemmati hailed the role of regular bond auctions in curbing the growth of ballooning money supply by reducing government dependence on the central bank for credit.
"If it was not for bonds, money supply would have expanded by an additional 5,600 trillion rials [$22.4 billion]," he said, addressing members of Fars Chamber of Commerce.
Banks have been asked to hold enough bonds to be able to operate in the interbank market and borrow from CBI under the newly-launched open market operation policy.
CBI has asked banks to buy bonds to be eligible to borrow. The Money and Credit Council, the top monetary decision-making body, has obliged lenders to allocate at least 3% of their financial resources to bonds.