The women have already served between three to eight years of their 25 to 30 year sentences handed down by state courts in Guanajuato state, activists said.
Veronica Cruz, director of the Centro Las Libres, which provides assistance to over 160 women facing abortion-related charges, said the organisation would appeal to the federal judiciary.
Of the six cases, one was a spontaneous abortion, two others were undertaken because of rape and the rest were for accidental pregnancies, Cruz said.
'All the men who got them pregnant abandoned them', she said.
Since the beginning of the decade, over 40 women have been put on trial for abortion, which is punishable by up to three years in prison under the penal code.
The legislation regarding abortion varies in Mexico's 32 separate jurisdictions. While in Mexico City it is legal, some states continue to treat abortion as a criminal offence.