Hi Dileep,
From a recent "Ask the Expert" event;
Q. Please I will like to know how many client running concurrently can the aironet 1500 AP hold in a wireless mesh Architecture on G/B frequency.
Here is an excellent answer from Cisco specialist Lily Chen;
A. Theoretically, you can have up to 256 clients per AP. However, you probably would not want to design to that, since that would be 256 clients sharing your wireless link. The recommended deployment will depend on the applications that are running on the network. Supporting data applications, you can plan to share the link across about 20 concurrent users on the root AP, with the maximum recommendation decreasing as you go deeper into the mesh (because the throughput is being shared by multiple nodes with many clients on each).
Here is a cisco doc that relates to this question;
Q. How many clients can associate to the AP?
A. The AP has the physical capacity to handle 2048 MAC addresses. However, because the AP is a shared medium and acts as a wireless hub, the performance of each user decreases as the number of users increases on an individual AP. Ideally, not more than 24 clients should associate with the AP because the throughput of the AP is reduced with each client that associates to the AP.
From this Q&A doc;
http://www.cisco.com/en/US/products/hw/wireless/ps430/products_qanda_item09186a008009483e.shtml
Have a look at this great thread that has some "Real World" answers from
Scott,Matthew,Mark and Emily (one of my all time favourite questions);
http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Wireless%20-%20Mobility&topic=WLAN%20Radio%20Standards&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1ddb85ec/0#selected_message
Hope this helps!
Rob