Mathers became the subject of an urban legend when it was falsely reported that he died in Vietnam. He served in Air Force's 22nd Air National Guard during the Vietnam War although he did remain in the United States. In 1969 (or 1968; sources differ) incorrect reports of his death were put out by Associated Press and United Press International when a similarly-named soldier was killed.

Mathers also starred in the spin off TV series Still the Beaver (1985), reprising his role as Theodore Cleaver. Early movies included This Is My Love (1954), Men of the Fighting Lady (1954), The Seven Little Foys (1955) and The Trouble with Harry (1955). Unable to keep up with the acting business as he moved into his teenage years, Mathers retired from it to concentrate on school. He suffered from dyslexia in his early life.

Mathers graduated from the University of California, Berkeley, with a BA degree in Philosophy in 1974. He began a successful career in real-estate development and banking. In order to pay for this, he used his savings from his acting career. In 1978 he reentered the entertainment business. He has since starred in "Better Luck Tomorrow" (2002) and "Playing Patti" (1998). He has also been in "Sexual Malice" (1994), "Down the Drain" (1990), and "It's Howdy Doody Time" (1987).

Today, he is a highly requested speaker at national conventions where he addresses the emotional state of the American family, using the fabled Cleavers from his early television career. He is also the father of three children: two daughters, Mercedes and Gretchen, and a son, Noah Mathers, who is currently in the United States Navy and has done some sound work with various movies. He was married twice, although is now divorced.