HONG KONG, April 21 (Reuters) - U.S. computer giant IBM (IBM.N: Quote, Profile, Research) shed more of its stake in top Chinese PC maker Lenovo Group Ltd (0992.HK: Quote, Profile, Research) on Monday, offloading $83.6 million worth of stock at a 6 percent discount to its last trading price, a source familiar with the deal said.

International Business Machines Corp (IBM) acquired its stake in Lenovo at HK$2.675 a share in 2005, when the Chinese firm bought IBM's ailing PC arm for $1.25 billion, and has been selling it off in chunks as lockup periods have lapsed.

On Monday, IBM sold 116.19 million Lenovo shares at HK$5.61 each, the bottom of their indicated range, in a deal handled by Citigroup (C.N: Quote, Profile, Research).

The stake represents 1.3 percent of Lenovo, the world's No. 4 personal computer maker, leaving IBM with 6.5 percent of the company, according to a document sent to investors.

Lenovo shares closed at HK$5.97 on Monday, down 0.5 percent, lagging a 2.17 percent gain in Hong Kong's benchmark Hang Seng Index .HSI.

In February, IBM sold $80 million worth of Lenovo shares at HK$5.41 each. (US$1=HK$7.8) (Reporting by Kennix Chim and Tony Munroe; Editing by Joseph Chaney/Elizabeth Fullerton)

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