The lawsuit accuses Jean Kasem of elder abuse and inflicting emotional distress on Kasem's children by restricting their access to him before his death, according to the AP news agency.
Kasem was known as host of the American Top 40 radio show and as the voice of Shaggy in the TV animation Scooby Doo.
He died last June at the age of 82.
He had been suffering from dementia, and the battle between his children from a previous marriage and their stepmother Jean began before his death.
They claim she abused him before he died, moved him from Santa Monica to Washington without telling them and, after his death, had him buried in an unmarked grave in Norway despite his wishes to be laid to rest in Los Angeles.
"What she did to my father is reprehensible," daughter Kerri Kasem said, according to AP. "It's disgusting. It's horrific."
Jean Kasem's lawyer H Michael Soroy did not immediately return a request for comment to the news agency.
Kerri Kasem said the family members were taking legal action after US prosecutors decided not to bring criminal charges against Jean Kasem, who was married to the star for more than 30 years.
In May, Los Angeles prosecutors said they could not prove at trial that her actions led to his death.
Kerri has taken out the lawsuit with siblings Julie and Michael Kasem and their uncle Mouner. They are seeking damages of $250,000 (Â£166,000).
But Kerri Kasem said: "We would rather see her in jail than receive one dime. We don't care about the money. We care about justice."
Casey Kasem began his career in the 1950s and found fame with the chart programme in the 1970s.
He famously ended his broadcasts with his signature sign-off: "Keep your feet on the ground and keep reaching for the stars."
Three of US DJ Casey Kasem's children and his brother have sued the late star's widow for wrongful death in the latest move in a bitter family feud.