Mohammed Haji Sadiq denies committing 15 child sex offences over a 10-year period.
Mr Sadiq, from the Cyncoed area of the city, taught Koran Studies at the Madina mosque between 1976 and 2006.
Cardiff Crown Court heard he "took advantage of his position".
He is accused of eight offences of sexual assault of a child under 13 by touching and seven offences of indecent assault.
The allegations involve four girls and are said to have taken place between 1996 and 2006 at the mosque, then situated on Woodville Road in the city.
The court heard the girls were aged between five and 11 at the time of the alleged offences.
The jury heard Mr Sadiq would touch the girls in intimate places.
Prosecuting barrister Susan Thomas said one of the alleged victims was told to lay face down on the defendant's lap, while he touched her bottom.
When interviewed by police the defendant said the allegations were made for political reasons within the mosque and that other allegations were for "financial motivation".
Mr Sadiq has had no involvement with the mosque since 2006.
The trial is due to last up to 10 days.
An 81-year-old man who taught at a Cardiff mosque created a culture where physical punishment "was the norm", a court has heard.