Bombs exploded at the Victory Monument in the afternoon, the site of protests. This was the second bomb attack on protestors since the operation to paralyse Bangkok was launched Jan 13 in a bid to oust Prime Minister Yingluck Shinawatra before the Feb 2 elections.
Thaworn Senneam, member of the People's Democratic Reform Committee and in-charge at the Victory Monument protest site, said a man threw bombs near the press centre and ran off, the Bangkok Post reported.
He was chased by security guards and protestors, prompting him to throw another bomb at them, said Thaworn.
Bombs exploded at the Victory Monument in the afternoon, the site of protests.
The injured people were rushed to hospitals.
Thaworn said the attacker was probably targeting him as the bomb exploded only 20 metres away from where he was standing.
Earlier, Thai opposition leader Suthep Thaugsuban said the caretaker government was responsible for the Friday attack on protestors, which injured 36 people in the area where Suthep was holding a march.
Yingluck denied Suthep's accusation that the government was behind the attack.
The protestors were demanding that no elections be held until implementation of major political reforms.
Since November, protestors have been taking to the streets and occupying government offices, calling for an end to Yingluck's government.
They accuse Yingluck of being a puppet of her brother, the ousted prime minister Thaksin Shinawatra, who was overthrown in a 2006 military coup.