The incident occurred close to Guiseley School, just before 3pm on Wednesday.
Officers investigating the report said they had today arrested a male in connection with the incident.
In a statement, West Yorkshire Police said: “On the 6th of September, West Yorkshire Police received a report of a sexual incident which had occurred near to Guiseley school just before 3pm that day.
“The investigation has been progressing since the time that it was reported.
“This morning your neighbourhood ward officers for the Guiseley area arrested a male on suspicion of the offence. At this time, the male is in custody and the investigation is ongoing.
“If you witnessed anything, or if you have any relevant information regarding the offence, please ring 101 and quote reference number 13170411896.”