Mr Somchai said the EC has not yet endorsed 19 senators-elect from the March 30 polls because complaints have been filed against their election, requiring investigation.
The EC on Tuesday announced the endorsement of new senators for 58 of the 77 provinces.
As for Khunying Jaruwan Maintaka, the winning candidate in Bangkok, there are four complaints against her. The investigation will be handled by the Bangkok election committee, he said.
Mr Somchai said he believed the EC would be able to endorse the remaining senators-elect by April 29, but not before April 18 when the Senate is scheduled to hold its first meeting.
The EC will endorse the election of all winning candidates within 30 days of the election, bar any that may have been disqualified, he said.
If by April 29 the investigation of some senators-elect had not been completed, the EC will go ahead and endorse their election. Their cases would then be forwarded to the Supreme Court's election cases division for a final decision within one year.
Asked about the plnned meeting with representatives of political parties on April 22, he said the EC will table the outcome of yesterday's meeting with the armed forces and security agencies for discussion at the meeting.
After that the results of the two meetings will be forwarded to a meeting with the government, probably late this month, to decide on an appropriate timeframe for a new general election, so that a draft royal decree for the new polls can be forwarded for royal approval, he said.
Mr Somchai said the EC has three options for the new general election, which may be held within 90, 120 or 150 days after the issuing of the royal decree.
A final decision has not been reached, pending consultation with the government, he said.