The man was detained for seven days and is accused of "deliberately spreading rumours in a time of war... to harm the military operations of our armed forces", the prosecutor's office said.
It did not reveal the identity of the man, who faces up to 10 years in jail if convicted, nor what he is accused of posting online.
Bahrain joined the Saudi-led coalition that in March launched air strikes against Iran-backed Houthi rebels who drove Yemen's government out of the country.
Read: Bomb kills two Bahraini policemen, government implicates Iran
Five Bahraini soldiers were killed in a missile strike against the coalition in Yemen on Friday, along with 45 Emirati and 10 Saudi troops.
In the United Arab Emirates meanwhile, prosecutors in Abu Dhabi ordered the arrest of an internet user who had posted an "incorrect" list of young Emiratis he claimed were among the 45 victims, local media reported Monday.
Emirati law provides for prison sentences and fines for those spreading rumours and false information, including about the armed forces, prosecutors said.
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