A system for monitoring user activity in an instant messaging session on a computer network periodically sends an activity message to other participants in the instant messaging session if the user has actively entered data during a first predetermined time interval. The system periodically sends a new activity message at intervals corresponding to the first predetermined time interval so long as the user is actively entering data during each time interval. If the user has not entered data during the first predetermined time interval, the system will not send an activity message. Other participants in the instant messaging session receive the activity message and generate an activity indicator on their respective displays. The computer receiving the activity message displays an activity indicator on the computer display in response to receipt of an activity message and starts a timer to measure a second predetermined time interval. If another activity message is not received within the second predetermined time interval, the activity indicator is deleted from the display.