unprompted (adj.)

• arbitrary
• automatic
• autonomous
• discretional
• discretionary
• elective
• free
• gratuitous
• impulsive
• independent
• instinctive
• involuntary
• nonmandatory
• optional
• self-acting
• spontaneous
• unasked
• uncalled-for
• uncoerced
• unconscious
• undesigned
• unforced
• unguarded
• unguided
• uninfluenced
• unintended
• unintentional
• uninvited
• unplanned
• unpremeditated
• unrequested
• unsolicited
• unsought
• unthinking
• unthought-of
• unwitting
• voluntary
• volunteer
• willful