Prime Minister Prayuth Chan-ocha, had earlier said that they could hold democratic elections in a year's time, at the end of 2015.
However, Finance Minister Sommai Phasee said it could take "a year and a half", BBC reported.
Phasee said: "As announced by the prime minister, it would take about one year. But, from my feeling, I think it may take, maybe, a year and a half."
The delay means that Thailand wouldn't return to democracy until the middle of 2016.
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Thailand's economy has been stagnant this year. After contracting at the start of the year, the economy has barely grown.
Justice Minister Paiboon Koomchaya had earlier said that martial law is here to stay.
On May 7, the country's top court ordered Prime Minister Yingluck Shinawatra and nine members of her cabinet to resign after charging them with abuse of power and violating the constitution.
Following which Prayuth seized power and became the country's prime minister, the first serving army officer to assume the top office in 22 years.