Producers say the two groups are mashing up to close out 2010 on the ABC special.
The two bands, who have melded their monikers to become NKOTBSB, performed together live for the first time on the Dick Clark-produced American Music Awards last month. The supergroup plans to tour North America together next summer.
"The NKOTBSB just keeps snowballing ... and nothing is as exciting as Times Square's New Year's countdown," the Backstreet Boys said Thursday.
"The excitement of this is just a glimpse of what our upcoming tour will be," the five members of New Kids on the Block added.
Pop singers Ke$ha and Taio Cruz are also set to perform from New York's Times Square on "Dick Clark's New Year's Rockin' Eve with Ryan Seacrest 2011," which begins at 10 p.m. EST on Dec. 31 and ends around 2 a.m. on Jan. 1.
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