Al Jazeera's Haru Mutasa, reporting from outside the court, said: "People across the country are concerned that if he wins the election, he will be facing criminal charges while he is the sitting president.
"[It's] a big concern for people [because it's] not good for the country, not good for investor confidence and not good for the general economy as the whole."
The ANC, which has ruled the country since the end of apartheid in 1994, is meanwhile facing the biggest challenge to its rule to date.
The Congress of the People (Cope), a splinter faction, is set to contest the election and has won some support among the electorate.
The September ruling that initially dismissed charges against Zuma also hinted at political interference from Thabo Mbeki, then the president of South Africa.
The ANC forced Mbeki out of office over the case, leading his supporters to form Cope.