JOHANNESBURG (Reuters) - South Africa's dominant mobile operator, Vodacom Group Ltd, reported a 1.7 percent increase in third-quarter revenue on Wednesday as it boosted the number of active customers.

The South African unit of Britain's Vodafone Group Plc, is fighting to maintain its market share in its key South African market and is keen to increase operations on the continent to diversify income.

The carrier said group revenue for the three months to end-December came in at 18.3 billion rand ($2.07 billion) from 18 billion rand the same period last year.

Active customers were up 12.2 percent to 51 million, the company said.

Vodacom is dwarfed on the continent by South African rival MTN Group Ltd and India's Bharti Airtel Ltd.

Vodacom shares are down 2 percent so far this year, lagging a 4 percent rise in the JSE Top 40 index.

(Reporting by Olivia Kumwenda; Editing by Matt Driskill)