The phrase "a regular mistake" is correct and usable in written English.
It can be used to describe a mistake that occurs frequently or is commonly made.
Example: "He often forgets to save his work, which is a regular mistake that could easily be avoided."
Alternatives: "a common error" or "a frequent mistake".
I have made regular mistakes on appointments.
"This is a street fight and you don't fight a street fight with a regular army, the same mistake that the Americans made.
And in a craft in which small errors are commonplace and bigger mistakes a regular occupational hazard, Ms. Toner devised a meticulous personal method for checking and re-checking names, dates, facts and figures in her own raw copy, a step few reporters take.
But in fact, most of us make this mistake on a regular basis – mostly because we don't have the time nor inclination to keep up with all of these rapid changes.
And like most of us in the thick of raising children, I routinely try to tell my kids -- and let's face it, I model this on a regular basis -- that people make mistakes and that mistakes aren't the worst thing in the world.
Machine translation mistakes are a regular occurrence for anyone using AI to translate languages, particularly ones with little relationship.
"We get calls on a regular basis where people have mistaken us for a soup kitchen or other women's social work service".
In the natural sciences, academics regularly kill their own interesting ideas in the pursuit of mundane truth, and admitting mistakes is a regular part of a scientist's life.
For some animals, homosexual behaviour isn't an occasional event – which we might put down to simple mistakes – but a regular thing.
She said Serco was making payroll mistakes on a regular basis, and most were down to "miscommunication, or people punching the wrong figures in".
