The blasts took place at around 8 pm near the busy shopping centre well visited by tourists and local residents, with police initially reporting they were caused by an electrical fault.
National police spokesman Prawut Thavornsiri told AFP further investigations had revealed the explosions were triggered by two IEDs (improvised explosive devices).
"Two homemade bombs exploded on a walkway between Siam BTS (skytrain) and Siam Paragon mall. They were hidden behind electric controls," he said, adding one man had received minor injuries. Further investigations are under way, he added, without providing more details.
An uneasy calm had descended upon the Thai capital since last May when the army seized power after months of often violent street protests that led to the ousting of ex-premier Yingluck Shinawatra's government.
Under martial law, political gatherings and criticism of the coup are forbidden, with the junta responding aggressively to any form of protest.