The toys were imported from China by Toys R Us Inc. of Wayne, N.J., and nationwide sold from August 2009 through September 2010 for about $25 each.
About 24,000 Imaginarium toys are involved in the recall.
The toys include a triangle-shaped frame that holds movable block letters on one side and a toy xylophone on another side.
The knobs attaching the xylophone keys to its frame can detach, posing a risk of choking, the regulator said.
Consumers were advised to stop using the "Imaginarium" and keep them out of reach of small children. They can be returned to Toys R Us for a refund or a store credit.
Consumers can call 800-869-7787 for information.