"The total office stock in Bangkok was 8.1 million square metres at the end of 2013 and the occupancy rate was 90.4 per cent," said James Pitchon, executive director of CBRE Research and Consulting.
"Rents rose 5-9 per cent year-on-year, depending on quality and location of the building."
The firm forecast office rents to rise further in the near future due to a limited number of new properties coming on the market by 2016.
The international real estate consultant said political unrest over the past four months, including daily anti-government protests in the capital, has had little impact on office occupancy rates.
"To date, we have seen no companies closing and no delays in ongoing leasing transactions, but we have seen a drop in enquiries," said Nithapat Tongpun, head office services at CBRE Thailand.
"Even if 2014 office demand is weak, rents are unlikely to fall because of the high occupancy levels and limited supply," he said.
Bangkok office rents are still among the cheapest in the region, costlier only than those of Manila, Wellington and Canberra.
Office rents in central Hong Kong are six times more expensive than in Bangkok.