Thank goodness for Izzy's correct answer. Yes, providing you are not symptomatic it's a perfectly normal healthy variant.
Of course it does depend in what situation this was taken in. If your BP is normally 140+ and all of a sudden it plummets to 90, then this may be indicative and in acute situations a plummet in BP could indicate shock
etc, so 'normal' and 'good' depends on the individual in question,conditions in which it was measured and other relevant factors such as age. If this is an average reading (or there abouts) it's completely normal.
Lower than average BP is only ever a problem if it's so low that it's unable to push blood around the body.