Is it considered a sin to unintentionally remove some eyebrow hair while drawing with an eyeliner pencil?

There is no harm in drawing the eyebrow with an eyeliner pencil or dyeing it a color similar to skin tone. If some eyebrow hair falls out unintentionally during this process, there is no blame upon you, as Allah Almighty says: (Our Lord, do not impose blame upon us if we forget or make a mistake) and (There is no blame upon you for what you have mistaken, but [there is blame for] what your hearts intended).